APPENDIX (continued 2)

This distribution of the seasons has a most important effect upon vegetation, to which sufficient attention has not been paid by cultivators of alpine Indian plants; in the first place, though English winters are cold enough for such, the summers are too hot and dry; and, in the second place, the great accession of temperature, causing the buds to burst in spring, occurs in the Himalaya in March, when the temperature at 7000 feet rises 8° above that of February, raising the radiating thermometer always above the freezing point, whence the young leaves are never injured by night frost: in England the corresponding rise is only 3°, and there is no such accession of temperature till May, which is 8° warmer than April; hence, the young foliage of many Himalayan plants is cut off by night frosts in English gardens early in the season, of which Abies Webbiana is a conspicuous example.

The greatest heat of the day occurs at Dorjiling about noon, owing to the prevalent cloud, especially during the rainy months, when the sun shines only in the mornings, if at all, and the clouds accumulate as the day advances. According to hourly observations of my own, it occurred in July at noon, in August at 1 p.m., and in September (the most rainy month) there was only four-tenths of a degree difference between the means of noon, 1 p.m., and 2 p.m., but I must refer to the abstracts at the end of this chapter for evidence of this, and of the wonderful uniformity of temperature during the rainy months. In the drier season again, after September, the greatest heat occurs between 2 and 3 p.m.; in Calcutta the hottest hour is about 2.45 p.m., throughout the year; and in England also about 3 p.m.

The hour whose temperature coincides with the mean of the day necessarily varies with the distribution of cloud and sunshine; it is usually about 7 a.m. and 7 p.m.; whereas in Calcutta the same coincidence occurs at a little before 10 a.m., and in England at about 8 a.m.

Next to the temperature of the air, observations on that of the earth are perhaps of the greatest value; both from their application to horticulture, and from the approximation they afford to the mean temperature of the week or month in which they are taken. These form the subject of a separate chapter.

Nocturnal and solar radiation, the one causing the formation of dew and hoar-frost when the air in the shade is above freezing, end killing plants by the rapid abstraction of heat from all their surfaces which are exposed to the clear sky, and the other scorching the skin and tender plants during the day, are now familiar phenomena, and particularly engaged my attention during my whole Indian journey. Two phenomena particularly obstruct radiation in Sikkim—the clouds and fog from the end of May till October, and the haze from February till May. Two months alone are usually clear; one before and one after the rains, when the air, though still humid, is transparent. The haze has never been fully explained, though a well-known phenomenon. On the plains of India, at the foot of the hills, it begins generally in the forenoon of the cold season, with the rise of the west wind; and, in February especially, obscures the sun’s disc by noon; frequently it lasts throughout the twenty-four hours, and is usually accompanied by great dryness of the atmosphere. It gradually diminishes in ascending, and have never experienced it at 10,000 feet; at 7000, however, it very often, in April, obscures the snowy ranges 30 miles off, which are bright and defined at sunrise, and either pale away, or become of a lurid yellow-red, according to the density of this haze, till they disappear at 10 a.m. I believe it always accompanies a south-west wind (which is a deflected current of the north-west) and dry atmosphere in Sikkim.

The observations for solar radiation were taken with a black-bulb thermometer, and also with actinometers, but the value of the data afforded by the latter not being fixed or comparative, I shall give the results in a separate section. (See Appendix K.) From a multitude of desultory observations, I conclude that at 7,400 feet, 125·7°, or +67° above the temperature of the air, is the average maximum effect of the sun’s rays on a black-bulb thermometer^[413] throughout the year, amounting rarely to +70° and +80° in the summer months, but more frequently in the winter or spring. These results, though greatly above what are obtained at Calcutta, are not much, if at all, above what may be observed on the plains of India. This effect is much increased with the elevation. At 10,000 feet in December, at 9 a.m., I saw the mercury mount to 132° with a difl: of +94°, whilst the temperature of shaded snow hard by was 22°; at 13,100 feet, in January, at 9 a.m., it has stood at 98°, diff. +68·2°; and at 10 a.m., at 114°, diff. +81·4°, whilst the radiating thermometer on the snow had fallen at sunrise to 0·7°. In December, at 13,500 feet, I have seen it 110°, diff. +84°; at 11 a.m., 11,500 feet; 122°, diff: +82°. This is but a small selection from many instances of the extraordinary power of solar radiation in the coldest months, at great elevations.

Nocturnal and terrestrial radiation are even more difficult phenomena for the traveller to estimate than solar radiation, the danger of exposing instruments at night being always great in wild countries. I most frequently used a thermometer graduated on the glass, and placed in the focus of a parabolic reflector, and a similar one laid upon white cotton,^[414] and found no material difference in the mean of many observations of each, though often 1° to 2° in individual ones. Avoiding radiation from surrounding objects is very difficult, especially in wooded countries. I have also tried the radiating power of grass and the earth; the temperature of the latter is generally less, and that of the former greater, than the thermometer exposed on cotton or in the reflector, but much depends on the surface of the herbage and soil.

The power of terrestrial, like that of solar radiation, increases with the elevation, but not in an equal proportion. At 7,400 feet, the mean of all my observations shows a temperature of 35·4°. During the rains, 3° to 4° is the mean maximum, but the nights being almost invariably cloudy, it is scarcely on one night out of six that there is any radiation. From October to December the amount is greater=10° to 12, and from January till May greater still, being as much as 15°. During the winter months the effect of radiation is often felt throughout the clear days, dew forming abundantly at 4000 to 8000 feet in the shaded bottoms of narrow valleys, into which the sun does not penetrate till 10 a.m., and from which it disappears at 3 p.m. I have seen the thermometer in the reflector fall 12° at 10 a.m. in a shaded valley. This often produces an anomalous effect, causing the temperature in the shade to fall after sunrise; for the mists which condense in the bottom of the valleys after midnight disperse after sunrise, but long before reached by the sun, and powerful radiation ensues, lowering the surrounding temperature: a fall of 1° to 2° after sunrise of air in the shade is hence common in valleys in November and December.^[415] The excessive radiation of the winter months often gives rise to a curious phenomenon; it causes the formation of copious dew on the blanket of the traveller’s bed, which radiates heat to the tent roof, and this inside either an open or a closed tent. I have experienced this at various elevations, from 6000 to 16,000 feet. Whether the minimum temperature be as high as 50°, or but little above zero, the effect is the same, except that hoar-frost or ice forms in the latter case. Another remarkable effect of nocturnal radiation is the curl of the alpine rhododendron leaves in November, which is probably due to the freezing and consequent expansion of the water in the upper strata of cells exposed to the sky. The first curl is generally repaired by the ensuing day’s sun, but after two or three nights the leaves become permanently curled, and remain so till they fall in the following spring.

I have said that the nocturnal radiation in the English spring months is the great obstacle to the cultivation of many Himalayan plants; but it is not therefore to be inferred that there is no similar amount of radiation in the Himalaya; for, on the contrary, in April its amount is much greater than in England, frequently equalling 13° of difference; and I have seen 16° at 7,500 feet; but the minimum temperature at the time is 51°, and the absolute amount of cold therefore immaterial. The mean minimum of London is 38°, and, when lowered 5·5° by radiation, the consequent cold is very considerable. Mr. Daniell, in his admirable essay on the climate of London, mentions 17° as the maximum effect of nocturnal radiation ever observed by him. I have registered 16° in April at Dorjiling; nearly as much at 6000 feet in February; twice 13°, and once 14·2° in September at 15,500 feet; and 10° in October at 16,800 feet; nearly 13° in January at 7000 feet; 14·5° in February at that elevation, and, on several occasions, 14·7° at 10,000 feet in November.

The annual rain-fall at Dorjiling averages 120 inches (or 10 feet), but varies from 100 to 130 in different years; this is fully three times the amount of the average English fall,^[416] and yet not one-fourth of what is experienced on the Khasia hills in Eastern Bengal, where fifty feet of rain falls. The greater proportion descends between June and September, as much as thirty inches sometimes falling in one month. From November to February inclusive, the months are comparatively dry; March and October are characterised by violent storms at the equinoxes, with thunder, destructive lightning, and hail.

The rain-gauge takes no account of the enormous deposition from mists and fogs: these keep the atmosphere in a state of moisture, the amount of which I have estimated at 0·88 as the saturation-point at Dorjiling, 0·83 being that of London. In July, the dampest month, the saturation-point is 0·97; and in December, owing to the dryness of the air on the neighbouring plains of India, whence dry blasts pass over Sikkim, the mean saturation-point of the month sometimes falls as low as 0·69.

The dew-point is on the average of the year 49·3°, or 3° below the mean temperature of the air. In the dampest month (July) the mean dew-point is only eight-tenths of a degree below the temperature, whilst in December it sinks 10° below it. In London the dew-point is on the average 5·6° below the temperature; none of the English months are so wet as those of Sikkim, but none are so dry as the Sikkim December sometimes is.

On the weight of the atmosphere in Sikkim; and its effects on the human frame.

Of all the phenomena of climate, the weight of the atmosphere is the most remarkable for its elusion of direct observation, when unaided by instruments. At the level of the sea, a man of ordinary bulk and stature is pressed upon by a superincumbent weight of 30,000 pounds or 13·5 tons. An inch fall or rise in the barometer shows that this load is lightened or increased, sometimes in a few hours, by nearly 1,000 pounds; and no notice is taken of it, except by the meteorologist, or by the speculative physician, seeking the subtle causes of epidemic and endemic complaints. At Dorjiling (7,400 feet), this load is reduced to less than 2,500 pounds, with no appreciable result whatever on the frame, however suddenly it be transported to that elevation. And the observation of my own habits convinced me that I took the same amount of meat, drink, sleep, exercise and work, not only without inconvenience, but without the slightest perception of my altered circumstances. On ascending to 14,000 feet, owing to the diminished supply of oxygen, exercise brings on vertigo and headache; ascending higher still, lassitude and tension across the forehead ensue, with retching, and a sense of weight dragging down the stomach, probably due to dilatation of the air contained in that organ. Such are the all but invariable effects of high elevations; varying with most persons according to the suddenness and steepness of the ascent, the amount and duration of exertion, and the length of time previously passed at great heights. After having lived for some weeks at 15,300 feet, I have thence ascended several times to 18,500, and once above 19,000 feet, without any sensations but lassitude and quickness of pulse;^[417] but in these instances it required great caution to avoid painful symptoms. Residing at 15,300 feet, however, my functions were wholly undisturbed; nor could I detect any quickness of pulse or of respiration when the body was at rest, below 17,000 feet. At that elevation, after resting a party of eight men for an hour, the average of their and my pulses was above 100°, both before and after eating; in one case it was 120°, in none below 80°.

Not only is the frame of a transient visitor unaffected (when at rest) by the pressure being reduced from 30,000 to 13,000 pounds, but the Tibetan, born and constantly residing at upwards of 14,000 feet, differs in no respect that can be attributed to diminished pressure, from the native of the level of the sea. The averaged duration of life, and the amount of food and exercise is the same; eighty years are rarely reached by either. The Tibetan too, however inured to cold and great elevations, still suffers when he crosses passes 18,000 or 19,000 feet high, and apparently neither more nor less than I did.

Liebig remarks (in his “Animal Chemistry”) that in an equal number of respirations,^[418] we consume a larger amount of oxygen at the level of the sea than on a mountain; and it can be shown that under ordinary circumstances at Dorjiling, 20·14 per cent. less is inhaled than on the plains of India. Yet the chest cannot expand so as to inspire more at once, nor is the respiration appreciably quickened; by either of which means nature would be enabled to make up the deficiency. It is true that it is difficult to count one’s own respirations, but the average is considered in a healthy man to be eighteen in a minute; in my own case it is sixteen, an acceleration of which by three or four could not have been overlooked, in the repeated trials I made at Dorjiling, and still less the eight additional inhalations required at 15,000 feet to make up for the deficiency of oxygen in the air of that elevation.

It has long been surmised that an alpine vegetation may owe some of its peculiarities to the diminished atmospheric pressure; and that the latter being a condition which the gardener cannot supply, he can never successfully cultivate such plants in general. I know of no foundation for this hypothesis; many plants, natives of the level of the sea in other parts of the world, and some even of the hot plains of Bengal, ascend to 12,000 and even 15,000 feet on the Himalaya, unaffected by the diminished pressure. Any number of species from low countries may be cultivated, and some have been for ages, at 10,000 to 14,000 feet without change. It is the same with the lower animals; innumerable instances may with ease be adduced of pressure alone inducing no appreciable change, whilst there is absence of proof to the contrary. The phenomena that accompany diminished pressure are the real obstacles to the cultivation of alpine plants, of which cold and the excessive climate are perhaps the most formidable. Plants that grow in localities marked by sudden extremes of heat and cold, are always very variable in stature, habit, and foliage. In a state of nature we say the plants “accommodate themselves” to these changes, and so they do within certain limits; but for one that survives of all the seeds that germinate in these inhospitable localities, thousands die. In our gardens we can neither imitate the conditions of an alpine climate, nor offer others suited to the plants of such climates.

The mean height of the barometer at Mr. Hodgson’s was 23·010, but varied 0·161 between July, when it was lowest, and October, when it was highest; following the monthly rise and fall of Calcutta as to period, but not as to amount (or amplitude); for the mercury at Calcutta stands in July upwards of half an inch (0·555 Prinsep) lower than it does in December.

The diurnal tide of atmosphere is as constant as to the time of its ebb and flow at Dorjiling as at Calcutta; and a number of very careful observations (made with special reference to this object) between the level of the plains of India, and 17,000 feet, would indicate that there is no very material deviation from this at any elevation in Sikkim. These times are very nearly 9.50 a.m. and about 10 p.m. for the maxima, the 9.50 a.m. very constantly, and the 10 p.m. with more uncertainty; and 4 a.m. and 4 p.m. for the minima, the afternoon ebb being most true to its time, except during the rains.

At 9.50 a.m. the barometer is at its highest, and falls till 4 p.m., when it stands on the average of the year 0·074 of an inch lower; during the same period the Calcutta fall is upwards of one-tenth of an inch (0·121 Prinsep).

It has been proved that at considerable elevations in Europe, the hours of periodic ebb and flow differ materially from those which prevail at the level of the sea; but this is certainly not the case in the Sikkim Himalaya.

The amplitude decreases in amount from 0·100 at the foot of the hills, to 0·074 at 7000 feet; and the mean of 132 selected unexceptionable observations, taken at nine stations between 8000 and 15,500 feet, at 9.50 a.m. and 4 p.m., gives an average fall of 0·056 of an inch; a result which is confirmed by interpolation from numerous horary observations at these and many other elevations, where I could observe at the critical hours.

That the Calcutta amplitude is not exceptionally great, is shewn by the register kept at different places in the Gangetic valley and plains of India, between Saharunpore and the Bay of Bengal. I have seen apparently trustworthy records of seven^[419] such, and find that in all it amounts to between 0·084 and 0·120 inch, the mean of the whole being 0·101 of an inch.

The amplitude is greatest (0·088) in the spring months (March, April, and May), both at Dorjiling and Calcutta: it is least at both in June and July, (0·027 at Dorjiling), and rises again in autumn (to ·082 in September).

The horary oscillations also are as remarkably uniform at all elevations, as the period of ebb and flow: the mercury falls slowly from 9.50 a.m. (when it is at its highest) till noon, then rapidly till 3 p.m., and slowly again till 4 p.m.; after which there is little change until sunset; it rises rapidly between 7 and 9 p.m., and a little more till 10 p.m.; thence till 4 a.m. the fall is inconsiderable, and the great rise occurs between 7 and 9 a.m.

It is well known that these fluctuations of the barometer are due to the expansion and contraction by heat and moisture of the column of atmosphere that presses on the mercury, in the cistern of the instrument: were the air dry, the effect would be a single rise and fall;^[420] the barometer would stand highest at the hottest of the twenty-four hours, and lowest at the coldest; and such is the case in arid continental regions which are perennially dry. That such would also be the case at Calcutta and throughout the Himalaya of Sikkim, is theoretically self-evident, and proved by my horary observations taken during the rainy months of 1848. An inspection of these at the end of this section (where a column contains the pressure of dry air) shows but one maximum of pressure, which occurs at the coldest time of the twenty-four hours (early in the morning), and one minimum in the afternoon. In the table of mean temperatures of the months, also appended to this section, will also be found a column allowing the pressure of dry air, whence it will be seen that there is but one maximum of the pressure of dry air, occurring at the coldest season in December, and one minimum, in July. The effect of the vapour is the same on the annual as upon the diurnal march of the pressure, producing a double maximum and minimum in the year in one case, and in the twenty-four hours in the other.

I append a meteorological register of the separate months, but at the same time must remind the reader that it does not pretend to strict accuracy. It is founded upon observations made at Dorjiling by Dr. Chapman in the year 1837, for pressure temperature and wet-bulb only; the other data and some modifications of the above are supplied from observations of my own. Those for terrestrial and nocturnal radiation are accurate as far as they go, that is to say, they are absolute temperatures taken by myself, which may, I believe, be recorded in any year, but much higher are no doubt often to be obtained. The dew-points and saturations are generally calculated from the mean of two day observations (10 a.m. and 4 p.m.) of the wet-bulb thermometer, together with the minimum, or are taken from observations of Daniell’s hygrometer; and as I find the mean of the temperature of 10 a.m., 4 p.m., and the minimum, to coincide within a few tenths with the mean temperature of the whole day, I assume that the mean of the wet-bulb observations of the same hours will give a near approach to that of the twenty-four hours. The climate of Dorjiling station has been in some degree altered by extensive clearances of forest, which render it more variable, more exposed to night frosts and strong sun-heat, and to drought, the drying up of small streams being one direct consequence. My own observations were taken at Mr. Hodgson’s house, elevated 7,430 feet, the position of which I have indicated at the commencement of this section, where the differences of climate due to local causes are sufficiently indicated to show that in no two spots could similar meteorological results be obtained. At Mr. Hodgson’s, for instance, the uniformity of temperature and humidity is infinitely more remarkable than at Dr. Chapman’s, possibly from my guarding more effectually against radiation, and from the greater forests about Mr. Hodgson’s house. I have not, however, ventured to interfere with the temperature columns on this account.

DORJILING METEOROLOGICAL REGISTER.

Jan. Feb. Mar. Apr. May June

Pressure of Atmosphere^[421] Range of Pressure Mean Shade Maximum Shade Maximum Sun Greatest Difference Mean Maximum Shade Minimum Shade Minimum Radiation Greatest Difference Mean Minimum Shade Mean Daily Range of Temps Sunk Thermometer Mean Dew-point Mean Dryness Force of Vapour Pressure of Dry Air Mean Saturation Rain in inches 23·307 ·072 40·0 56·0 119·0 72·0 47·2 29·0 16·0 12·7 32·8 14·4 46·0 34·3 5·1 ·216 23·091 ·84 1·72 23·305 ·061 42·1 57·0 124·0 78·0 50·0 25·5 23·0 15·3 34·2 15·8 48·0 37·2 3·9 ·239 23·066 ·87 0·92 23·307 ·083 50·7 66·5 120·0 60·0 58·4 37·0 27·8 8·7 43·1 15·3 50·0 45·8 5·8 ·323 23·084 ·82 1·12 23·280 ·085 55·9 68·5 125·0 66·0 63·7 38·0 33·0 16·0 48·1 15·6 58·0 49·8 6·6 ·371 22·909 ·80 2·52 23·259 ·088 57·6 69·0 125·0 65·0 65·3 38·0 40·0 10·0 50·0 15·3 61·0 54·4 2·7 ·434 22·825 ·91 9·25 23·207 ·067 61·2 71·0 126·2 62·2 66·7 51·5 47·0 4·8 55·8 10·9 62·0 59·5 2·0 ·515 22·692 ·93 26·96

July Aug. Sept. Oct. Nov. Dec. Mean

Pressure of Atmosphere^[421] Range of Pressure Mean Shade Maximum Shade Maximum Sun Greatest Difference Mean Maximum Shade Minimum Shade Minimum Radiation Greatest Difference Mean Minimum Shade Mean Daily Range of Temps Sunk Thermometer Mean Dew-point Mean Dryness Force of Vapour Pressure of Dry Air Mean Saturation Rain in inches 23·203 ·062 61·4 69·5 130·0 62·0 65·5 56·0 52·0 3·5 57·3 8·2 62·2 60·7 0·8 ·535 22·668 ·97 25·34 23·230 ·070 61·7 70·0 133·0 62·0 66·1 54·5 50·0 3·5 57·4 8·7 62·0 60·4 1·1 ·530 22·700 ·96 29·45 23·300 ·082 59·9 70·0 142·0 70·0 64·7 51·5 47·5 10·0 55·2 9·5 61·0 58·5 1·4 ·498 22·802 ·95 15·76 23·372 ·075 58·0 68·0 133·0 65·0 66·5 43·5 32·0 12·0 49·5 17·0 60·0 52·5 4·2 ·407 22·865 ·86 8·66 23·330 ·078 50·0 63·0 123·0 68·0 56·5 38·0 30·0 12·0 43·5 13·0 55·0 46·5 3·2 ·331 22·999 ·90 0·11 23·365 ·062 43·0 56·0 108·0 77·2 51·6 32·5 26·0 10·0 34·9 16·7 49·0 31·8 10·6 ·198 23·165 ·69 0·45 22·289 ·074 53·5 65·4 125·7 67·3 60·2 41·3 35·4 9·9 46·8 13·4 56·2 49·4 4·0 ·383 22·906 ·88 Sum 122·26

Horary Observations at Jillapahar, Dorjiling, Alt. 7,430 feet. JULY, 1848

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air

7 23 27 22 20 26 12 11 25 23 13 10 6 6 22 6 6 19 1 a.m. 8 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 22·877 ·882 ·884 +·899 ·899 ·884 ·876 ·866 ·852 ·846 –·840 ·845 ·853 ·867 ·878 ·885 +·887 ·887 59·6 62·1 62·6 63·5 64·1 65·0 64·1 64·4 64·8 64·1 64·7 63·7 62·7 61·0 60·7 60·5 60·2 59·8 58·9 60·6 61·3 61·7 62·3 63·1 61·7 61·0 62·6 61·7 64·0 61·5 61·1 59·5 59·4 59·5 59·2 59·1 0·7 1·5 1·3 1·8 1·8 1·9 2·4 3·4 2·2 2·4 0·7 2·2 1·6 1·5 1·3 1·0 1·0 0·7 ·504 ·534 ·546 ·554 ·565 ·580 ·566 ·541 ·571 ·554 ·597 ·549 ·542 ·515 ·512 ·514 ·508 ·507 5·65 6·03 6·10 6·12 6·27 6·44 6·13 6·00 6·32 6·13 6·62 6·12 6·03 5·74 5·72 5·75 5·70 5·68 ·988 ·950 ·960 ·945 ·945 ·940 ·923 ·892 ·930 ·924 ·978 ·928 ·948 ·952 ·960 ·968 ·965 ·975 22·373 ·348 ·338 ·345 ·334 ·304 ·310 ·325 ·281 ·292 –·243 ·296 ·311 ·352 ·366 ·371 ·379 +·382

AUGUST

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air

15 26 28 28 24 23 21 21 21 19 19 19 19 19 19 19 19 19 1 a.m. 8 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 22·909 ·904 ·915 +·917 ·915 ·905 ·898 ·884 ·873 ·855 –·853 ·863 ·865 ·878 ·890 +·893 ·892 ·889 59·8 62·1 63·1 64·3 64·7 64·7 65·3 65·0 64·8 63·9 63·2 62·3 61·6 61·1 60·7 60·3 60·1 60·0 59·5 61·5 61·9 62·7 63·1 63·4 63·3 63·4 63·1 62·4 61·7 60·8 60·4 60·2 60·0 59·7 59·7 59·4 0·3 0·6 1·2 1·6 1·6 1·3 2·0 1·6 1·7 1·5 1·5 1·5 1·2 0·9 0·7 0·6 0·4 0·6 ·514 ·549 ·558 ·572 ·580 ·586 ·584 ·586 ·579 ·568 ·554 ·538 ·531 ·527 ·523 ·518 ·517 ·513 5·70 6·13 6·20 6·35 6·42 6·50 6·48 6·50 6·43 6·30 6·15 6·00 5·92 5·88 5·85 5·78 5·79 5·73 ·992 ·980 ·962 ·950 ·948 ·958 ·940 ·950 ·943 ·952 ·952 ·952 ·962 ·970 ·976 ·980 ·988 ·980 +22·395 ·355 ·357 ·345 ·335 ·319 ·314 ·298 ·294 –·287 ·299 ·325 ·334 ·351 ·367 ·375 ·375 ·376

SEPTEMBER

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air

28 29 28 24 23 23 23 23 23 19 19 20 21 22 24 24 23 8 a.m. 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 23·000 ·013 +·018 ·009 22·995 ·980 ·962 ·947 –·944 ·944 ·948 ·958 ·975 ·986 +·991 ·989 ·994 59·2 60·1 60·8 61·6 62·4 62·7 62·8 62·3 61·8 60·3 59·4 58·7 58·2 57·8 57·4 57·0 56·7 58·1 58·5 59·5 60·0 60·5 60·5 60·4 60·0 59·9 58·6 58·4 57·4 57·0 56·6 56·4 55·9 55·4 1·1 1·6 1·3 1·6 1·9 2·2 2·4 2·3 1·9 1·7 1·0 1·3 1·2 1·2 1·0 1·1 1·3 ·492 ·497 ·514 ·523 ·533 ·532 ·531 ·522 ·521 ·498 ·496 ·479 ·473 ·467 ·463 ·456 ·449 5·50 5·57 5·77 5·83 5·93 5·92 5·90 5·83 5·82 5·58 5·58 5·60 5·33 5·25 5·23 5·15 5·07 ·968 ·945 ·958 ·950 ·942 ·942 ·925 ·924 ·940 ·940 ·968 ·960 ·962 ·960 ·968 ·962 ·927 22·508 ·526 ·504 ·506 ·462 ·448 ·431 ·425 –·423 ·446 ·452 ·479 ·502 ·519 ·528 ·533 +·545

OCTOBER (22 days)

No. of Obser- vations Hour Baro- meter corrected Temp. Air Dew Point Diff. Tension of Vapour Weight of Vapour Humi- dity Pressure of Dry Air

11 19 20 20 19 13 15 13 13 14 16 13 6 7 3 7 14 18 14 6-6.30 7 a.m. 8 9 10 11 Noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 Midnight 23·066 ·072 ·086 ·099 +·100 ·079 ·072 ·055 ·033 ·027 ·024 –·022 ·033 ·045 ·038 ·061 +·072 ·067 ·068 54·4 54·3 55·2 56·3 57·1 57·6 57·9 58·0 57·7 57·9 57·9 56·6 55·9 55·4 53·7 55·1 54·6 54·5 54·1 52·7 52·3 53·7 54·4 55·5 55·6 56·1 56·4 56·6 56·2 56·1 54·8 54·4 53·8 53·3 54·1 53·0 53·0 52·8 1·7 2·0 1·5 1·9 1·6 2·0 1·8 1·6 1·1 1·7 1·8 1·8 1·5 1·6 0·4 1·0 1·6 1·5 1·3 ·409 ·403 ·423 ·434 ·450 ·451 ·459 ·463 ·466 ·460 ·458 ·439 ·433 ·424 ·417 ·429 ·413 ·413 ·411 4·65 4·58 4·78 4·90 5·07 5·08 5·15 5·17 5·25 5·16 5·15 4·98 4·90 4·80 4·75 4·83 4·82 4·82 4·65 ·943 ·025 ·950 ·935 ·942 ·935 ·940 ·950 ·962 ·940 ·940 ·948 ·950 ·950 ·990 ·965 ·949 ·950 ·962 22·657 +·669 ·663 ·665 ·650 ·728 ·613 ·592 ·567 ·567 ·–·566 ·583 ·600 ·621 ·621 ·632 ·659 ·654 ·657

G. ON THE RELATIVE HUMIDITY, AND ABSOLUTE AMOUNT OF VAPOUR CONTAINED IN THE ATMOSPHERE AT DIFFERENT ELEVATIONS IN THE SIKKIM HIMALAYA.

My observations for temperature and wet-bulb being for the most part desultory, taken at different dates, and under very different conditions of exposure, etc., it is obvious that those at one station are hardly, if at all, comparative with those of another, and I have therefore selected only such as were taken at the same date and hour with others taken at the Calcutta Observatory, or as can easily be reduced; which thus afford a standard (however defective in many respects) for a comparison. I need hardly remind my reader that the vapour-charged wind of Sikkim is the southerly one, which blows over Calcutta; that in its passage northwards to Sikkim in the summer months, it traverses the heated plains at the foot of the Himalaya, and ascending that range, it discharges the greater part of its moisture (120 to 140 inches annually) over the outer Himalayan ranges, at elevations of 4000 to 8000 feet. The cooling effect of the uniform covering of forest on the Sikkim ranges is particularly favourable to this deposition, but the slope of the mountains being gradual, the ascending currents are not arrested and cooled so suddenly as in the Khasia mountains, where the discharge is consequently much greater. The heating of the atmosphere, too, over the dry plains at the foot of the outer range, increases farther its capacity for the retention of vapour, and also tends to render the rain-fall less sudden and violent than on the Khasia, where the south wind blows over the cool expanse of the Jheels. It will be seen from the following observations, that in Sikkim the relative humidity of the atmosphere remains pretty constantly very high in the summer months, and at all elevations, except in the rearward valleys; and even there a humid atmosphere prevails up to 14,000 feet, everywhere within the influence of the snowy mountains. The uniformly high temperature which prevails throughout the summer, even at elevations of 17,000 and 18,000 feet, is no doubt proximately due to the evolution of heat during the condensation of these vapours. It will be seen by the pages of my journal, that continued sunshine, and the consequent heating of the soil, is almost unknown during the summer, at any elevation on the outer or southward ranges of Dorjiling: but the sunk thermometer proves that in advancing northward into the heart of the mountains and ascending, the sun’s effect is increased, the temperature of the earth becoming in summer considerably higher than that of the air. With regard to the observations themselves, they may be depended upon as comparable with those of Calcutta, the instruments having been carefully compared, and the cases of interpolation being few. The number of observations taken at each station is recorded in a separate column; where only one is thus recorded, it is not to be regarded as a single reading, but the mean, of several taken during an hour or longer period. I have rejected all solitary observations, even when accompanied by others at Calcutta; and sundry that were, for obvious reasons, likely to mislead. Where many observations were taken at one place, I have divided them into sets, corresponding to the hours at which alone the Calcutta temperature and wet-bulb thermometer are recorded,^[423] in order that meteorologists may apply them to the solution of other questions relating to the distribution of heat and moisture. The Dorjiling observations, and those in the immediate neighbourhood of that station, appeared to me sufficiently numerous to render it worth while classing them in months, and keeping them in a series by themselves. The tensions of vapour are worked from the wet-bulb readings by Apjohn’s formula and tables, corrected for the height of the barometer at the time. The observations, except where otherwise noted, are taken by myself.

SERIES I. Observations made at or near Dorjiling. JANUARY, 1849

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

15 15 10 8 9 The Dale,^[424] Mr. Muller’s … … … 6956 … … … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset 42·9 45·8 48·3 48·6 46·5 32·4 33·8 37·4 37·8 37·1 10·5 12·0 10·9 10·8 9·4 ·202 ·212 ·241 ·244 ·238 67·5 72·9 76·1 75·1 71·8 55·3 55·7 55·1 54·8 54·9 12·2 17·2 21·0 20·3 16·9 ·446 ·455 ·444 ·440 ·441

57 … … Mean 46·4 35·7 10·7 ·227 72·7 55·2 17·5 ·445

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·700 2·63 gr. 0·562 4·86 gr.

JANUARY, 1850

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

3 6 3 5 5 5 13 4 1 Jillapahar, Mr. Hodgson’s … … … … … Saddle of road at Sinchul Pacheem 7430 … … … … … … 7412 7258 Sunrise 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset Miscel. Do. Do. 32·8 39·5 42·4 41·9 41·1 38·7 41·9 41·1 39·8 30·1 34·7 38·0 37·8 38·5 35·6 39·9 36·4 38·7 2·7 4·8 4·4 4·1 2·6 3·1 2·0 4·7 1·1 ·186 ·219 ·246 ·244 ·250 ·226 ·263 ·233 ·252 51·5 66·9 74·1 78·3 77·4 72·4 77·9 67·7 71·6 48·5 55·1 51·7 51·4 59·5 54·7 60·1 57·2 50·5 3·0 11·8 22·4 26·9 17·9 17·7 17·8 10·5 21·1 ·354 ·444 ·395 ·391 ·514 ·438 ·525 ·476 ·379

45 … … Mean 39·9 36·6 3·3 ·235 70·9 54·3 16·6 ·435

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·890 2·75 gr. 0·580 4·86 gr.

FEBRUARY, 1850

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

6 18 12 12 17 19 13 Jillapahar … … … … … The Dale^[425] 7430 … … … … … 6956 Sunrise 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset Misc. 36·9 42·9 44·8 44·8 44·0 42·4 40·8 34·7 38·6 41·3 37·4 35·6 35·8 35·1 2·2 4·3 3·5 7·4 8·4 6·6 5·7 ·219 ·251 ·276 ·241 ·226 ·228 ·222 60·0 72·8 79·8 82·4 81·1 76·3 69·9 54·2 58·8 58·7 57·9 58·1 60·7 59·8 5·8 14·0 21·1 24·5 23·0 15·6 10·1 ·431 ·503 ·501 ·487 ·492 ·536 ·518

97 … … Mean 42·4 36·9 5·4 ·238 74·6 58·3 16·3 ·495

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·828 2·75 gr. 0·590 5·40 gr.

MARCH, 1850

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

10 8 5 8 6 3 Jillapahar … … … … Pacheem 7430 … … … … 7258 9.50 a.m. Noon 2.40 p.m. 4 p.m. Sunset Miscel. 44·2 45·5 46·4 45·5 43·1 44·8 42·7 43·0 44·0 43·4 41·5 44·6 1·5 2·5 2·4 2·1 1·6 0·2 ·290 ·293 ·303 ·297 ·278 ·310 81·6 88·2 91·3 90·1 82·9 85·0 64·1 57·0 53·2 52·0 63·7 74·8 17·5 31·2 38·1 38·1 19·2 10·2 ·602 ·472 ·416 ·399 ·590 ·848

40 … … Mean 44·9 43·2 1·7 ·295 86·5 60·8 25·7 ·555

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·940 3·42 gr. 0·438 5·72 gr.

APRIL

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

3 3 1 7 2 4 3 Jillapahar, 1849 … … Dr. Campbell’s, 1850 … … … 7430 … … 6932 … … … 9.50 a.m. Noon 2.40 p.m. 9.50 a.m. Noon 4 p.m. 57·0 59·8 60·2 61·8 65·4 57·5 56·9 40·2 44·1 44·4 53·3 52·8 53·7 51·4 16·8 15·7 15·8 8·5 12·6 3·8 5·5 ·266 ·305 ·308 ·417 ·411 ·423 ·392 90·3 97·0 97·7 86·7 91·3 88·6 82·8 71·3 64·5 73·4 66·3 68·8 72·1 73·0 19·0 32·5 24·3 20·4 22·5 16·5 9·8 ·758 ·607 ·812 ·644 ·699 ·778 ·800

23 … … Mean 59·8 48·6 11·3 ·360 90·6 69·9 20·7 ·728

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·684 3·98 gr. 0·523 7·65 gr.

MAY

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

3 45 Smith’s Hotel, 1848 Colinton,^[426] 1849 6863 7179 Miscel. Miscel. 57·2 60·4 55·0 57·9 2·2 1·5 ·443 ·466 88·6 90·0 78·4 77·2 10·2 12·8 ·951 ·917

48 … Mean 58·8 56·5 2·4 ·455 89·3 77·8 11·5 ·934

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·926 5·22 gr. 0·698 9·90 gr.

JUNE

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

40 Colinton,^[427] 7179 Miscel. 60·9 57·6 3·3 ·483 85·5 78·4 7·1 ·952

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·895 5·39 gr. 0·800 10·17 gr.

JULY, 1848

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

18 25 24 16 31 31 31 Jillapahar … … … The Dale,^[428] … … 7430 … … … 6952 … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. 6 a.m. 2 p.m. 6 p.m. 63·2 65·0 64·7 63·8 60·2 66·3 63·0 61·4 62·6 62·3 61·5 58·7 63·3 60·9 1·8 2·4 2·4 2·3 1·5 3·0 2·1 ·548 ·570 ·565 ·550 ·537 ·621 ·575 87·0 89·0 88·1 87·2 81·3 88·0 84·8 79·4 80·0 79·4 79·5 79·0 79·6 79·2 7·6 9·0 8·7 7·7 2·3 8·4 5·6 ·983 1·001 ·983 ·985 ·969 ·989 ·977

176 … … Mean 63·7 61·5 2·2 ·567 86·5 79·4 7·0 ·984

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·929 6·06 gr. 0·800 10·45 gr.

AUGUST, 1848

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

23 21 17 13 31 31 31 Jillapahar … … … The Dale,^[429] … … 7430 … … … 6952 … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. 6 a.m. 2 p.m. 6 p.m. 64·2 64·7 64·7 63·9 60·5 65·3 62·8 62·4 63·3 62·8 62·5 59·5 63·6 61·8 1·8 1·4 1·9 1·4 1·0 1·7 1·0 ·567 ·584 ·574 ·568 ·551 ·628 ·591 85·8 87·2 87·4 86·5 80·8 87·2 83·7 79·1 79·2 79·3 79·5 78·8 79·2 78·7 6·7 8·0 8·1 7·0 2·0 8·0 5·0 ·973 ·976 ·979 ·984 ·962 ·976 ·959

167 … … Mean 63·7 62·3 1·5 ·580 85·5 79·1 6·4 ·973

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·995 6·25 gr. 0·818 10·35 gr.

SEPTEMBER, 1848

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

28 23 23 21 30 30 30 Jillapahar … … … The Dale,^[430] … … 7430 … … … 6952 … … 9.50 a.m. Noon 2.40 p.m. 4 p.m. 6 a.m. 2 p.m. 6 p.m. 60·8 62·4 62·4 62·0 57·4 64·9 60·8 59·3 60·3 59·6 59·6 56·2 60·8 59·0 1·5 2·1 2·8 2·4 1·2 4·1 1·8 ·511 ·528 ·516 ·516 ·495 ·573 ·543 87·0 88·5 88·1 86·9 80·9 88·8 84·7 78·4 78·1 77·4 77·1 78·3 77·4 76·6 8·6 10·4 10·7 9·8 2·6 11·4 8·1 ·952 ·943 ·922 ·914 ·948 ·923 ·899

185 … … Mean 61·5 59·3 2·3 ·526 86·4 77·6 8·8 ·929

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·932 5·72 gr. 0·760 9·88 gr.

OCTOBER, 1848

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

6 6 6 4 8 8 17 19 Jillapahar … … Goong. Ditto The Dale,^[431] … … 7430 … … 7436 7441 6952 … … Noon 2.40 p.m. 4 p.m. Misc. Misc. 6 a.m. 2 p.m. 6 p.m. 55·9 55·7 55·6 48·3 51·2 55·2 61·4 56·9 55·3 54·9 54·9 48·3 50·2 52·7 56·3 54·2 0·6 0·8 0·7 0 1·0 2·5 5·1 2·7 ·446 ·440 ·441 ·352 ·376 ·439 ·497 ·463 84·4 86·0 85·2 81·2 80·7 76·1 87·0 82·8 75·3 73·3 74·4 73·7 66·9 74·2 71·2 73·9 9·1 12·7 10·8 7·5 13·8 1·9 15·8 8·9 ·863 ·808 ·837 ·819 ·657 ·834 ·756 ·824

74 … … Mean 55·0 53·4 1·7 ·432 82·9 72·9 10·1 ·800

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·950 4·74 gr. 0·658 8·55 gr.

NOVEMBER AND DECEMBER, 1848

DORJILING CALCUTTA

No. of Obs. Place Elev. (feet) Hour Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

4 8 6 9 19 The Dale^[432] Nov./Dec. … December … 6952 … … … … 6 a.m. 2 p.m. 6 p.m. 2 p.m. 6 a.m. 45·6 60·0 50·6 49·7 44·0 41·4 48·3 44·7 41·7 40·5 4·2 11·7 5·9 8·0 3·5 ·277 ·355 ·311 ·280 ·269 67·9 83·3 77·3 79·3 75·8 64·7 65·2 63·1 59·0 62·6 3·2 18·1 14·2 20·3 13·2 ·610 ·621 ·579 ·505 ·569

46 … … Mean 49·9 43·3 6·7 ·298 76·7 62·9 13·8 ·577

Dorjiling Calcutta

Humidity Vapour in cubic foot of atmosphere 0·798 3·40 gr. 0·640 6·27 gr.

Comparison of Dorjiling and Calcutta.

HUMIDITY WEIGHT OF VAPOUR IN CUBIC FOOT OF AIR

No. of Obs. Month Dorjiling Calcutta Diff. Dorjiling Dorjiling Calcutta Diff. Calcutta

102 97 40 23 48 40 176 167 185 74 46 January February March April May June July August September October Nov. and Dec. –·795 ·828 ·940 ·684 ·926 ·895 ·929 +·955 ·932 ·950 ·798 ·572 ·590 –·438 ·523 ·698 ·800 ·800 +·818 ·760 ·658 ·640 +·224 +·238 +·502 +·161 +·228 +·095 +·129 +·136 +·172 +·292 +·158 –2·68 2·75 3·42 3·98 5·22 5·39 6·06 +6·25 5·72 4·74 6·27 –4.80 5·40 5·72 7·65 9·90 10·17 10·05 +10·35 9·88 8·55 6·27 +2·12 +2·65 +2·30 +3·67 +4·62 +4·78 +3·99 +4·10 +4·16 +3·81 +2·87

998 Mean 0·876 0·663 +·212 4·51 8·07 +3·55

It is hence evident, from nearly 1000 comparative observations, that the atmosphere is relatively more humid at Dorjiling than at Calcutta, throughout the year. As the southerly current, to which alone is due all the moisture of Sikkim, traverses 200 miles of land, and discharges from sixty to eighty inches of rain before arriving at Dorjiling, it follows that the whole atmospheric column is relatively drier over the Himalaya than over Calcutta; that the absolute amount of vapour, in short, is less than it would otherwise be at the elevation of Dorjiling, though the relative humidity is so great. A glance at the table at the end of this section appears to confirm this; for it is there shown that, at the base of the Himalaya, at an elevation of only 250 feet higher than Calcutta, the absolute amount of vapour is less, and of relative humidity greater, than at Calcutta.

SERIES II. Observations at various Stations and Elevations in the Himalaya of East Nepal and Sikkim. ELEVATION 735 TO 2000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

3 2 1 3 1 6 1 5 5 11 10 Katong Ghat, Teesta river Great Rungeet, at bridge Ditto Tambur river, E. Nepal Ditto Bhomsong, Teesta river Ditto Little Rungeet Pemiongchi, Great Rungeet Punkabaree Ditto Guard house (Gt. Rungeet) 735 818 818 1388 1457 1596 1596 1672 1840 1850 1850 1864 Dec. April May Nov. Nov. Dec. May Jan. Dec. March May April 60·2 82·8 77·8 60·6 64·2 58·6 68·2 51·0 54·6 70·1 73·5 73·7 55·3 63·5 60·3 57·0 59·1 52·0 66·4 50·2 53·7 55·6 68·3 63·8 4·9 19·3 17·5 3·6 5·1 6·6 1·8 0·8 0·9 14·5 5·2 9·9 ·447 ·588 ·528 ·473 ·507 ·399 ·647 ·377 ·424 ·472 ·687 ·592 73·2 95·8 91·7 73·3 77·3 71·6 82·6 58·5 73·5 79·2 83·7 92·4 56·7 61·9 78·3 62·7 63·4 57·0 77·4 58·0 66·2 62·6 77·9 67·0 16·5 33·9 13·4 10·6 13·9 14·6 5·2 0·5 7·3 16·6 5·8 25·4 ·468 ·557 ·947 ·571 ·585 ·474 ·923 ·489 ·642 ·570 ·938 ·660

48 Mean 66·3 58·8 7·5 ·512 79·4 65·8 13·6 ·652

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·717 5·57 gr. 0·663 6·88 gr.

ELEVATION 2000 TO 3000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

2 8 3 3 2 8 12 8 3 Singdong Mywa Guola, E. Nepal Pemmi river, E. Nepal Tambur river, E. Nepal Blingbong (Teesta) Lingo (Teesta) Serriomsa (Teesta) Lingmo (Teesta) Ditto 2116 2132 2256 2545 2684 2782 2820 2849 2952 Dec. Nov. Nov. Nov. May May Dec. May Dec. 60·5 66·2 55·6 57·3 72·6 75·8 64·1 68·6 56·4 53·4 57·5 53·9 51·6 64·0 67·3 56·8 64·6 53·5 7·1 8·7 1·7 5·7 8·6 8·5 7·3 4·0 2·9 ·419 ·481 ·426 ·394 ·597 ·666 ·469 ·610 ·420 72·1 75·7 62·9 75·0 81·7 90·7 70·8 87·9 69·5 52·9 68·7 62·3 63·7 73·6 77·7 62·4 74·9 66·5 19·2 7·0 0·6 11·3 8·1 13·0 8·4 13·0 3·0 ·411 ·697 ·566 ·591 ·817 ·932 ·567 ·851 ·647

49 Mean 64·1 58·1 6·1 ·498 76·3 67·0 9·3 ·675

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·820 5·45 gr. 0·740 7·13 gr.

ELEVATION 3000 TO 4000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

5 9 3 2 2 7 7 1 3 1 1 2 5 Kulhait river Ratong river Tambur river Chingtam Tikbotang Myong Valley Iwa river Ratong river Tukcham Pacheem village Yankoong Mikk Sunnook 3159 3171 3201 3404 3763 3782 3783 3790 3849 3855 3867 3912 3986 Jan. Jan. Nov. Nov. Dec. Oct. Dec. Jan. Nov. Jan. Dec. May Dec. 49·8 44·2 53·0 54·8 56·5 61·4 47·5 56·2 68·8 54·5 50·0 66·1 47·9 47·0 43·0 50·0 49·0 53·4 58·4 45·6 41·1 65·4 46·3 43·6 63·9 45·5 2·8 1·2 3·0 5·8 3·1 3·0 1·9 15·1 3·4 8·2 6·4 2·2 2·4 ·337 ·294 ·373 ·360 ·419 ·496 ·321 ·275 ·625 ·329 ·299 ·595 ·320 65·8 69·9 72·9 74·9 68·0 80·7 73·3 75·8 83·7 73·6 69·1 84·3 69·4 57·3 56·6 63·2 73·0 61·8 71·2 64·7 53·0 76·8 59·4 63·8 75·1 61·1 8·5 13·3 9·7 1·9 6·2 9·5 8·6 22·8 6·9 14·2 5·3 9·2 8·3 ·477 ·466 ·582 ·802 ·555 ·755 ·611 ·414 ·904 ·513 ·593 ·856 ·542

48 Mean 54·7 50·2 4·5 ·388 74·0 64·4 9·6 ·621

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·858 4·23 gr. 0·732 6·60 gr.

ELEVATION 4000 TO 5000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

3 4 2 3 7 3 6 7 10 5 5 2 16 6 4 4 2 4 7 6 3 6 11 9 Yangyading Gorh Namgah Taptiatok (Tambur) Myong Valley Jummanoo Nampok Chakoong Singtam Namten Purmiokshong Rungniok Singtam Cheadam Sablakoo Bheti Temi Lingtam Khersiong Ditto Tassiding Lingcham Dikkeeling Tchonpong 4111 4128 4229 4283 4345 4362 4377 4407 4426 4483 4521 4565 4575 4653 4676 4683 4771 4805 4813 4813 4840 4870 4952 4978 Dec. May Oct. Nov. Oct. Nov. Dec. May May Dec. Nov. Jan. Oct/Nov. Dec. Dec. Nov. May May Jan. Mar. Dec. Dec. Dec. Jan. 52·0 66·4 57·2 51·3 59·1 60·4 49·6 57·8 62·4 44·7 60·5 54·7 63·8 51·4 50·1 59·0 59·8 60·4 51·0 53·6 52·0 48·5 62·0 49·4 43·6 59·0 54·1 45·8 57·8 50·0 49·1 57·6 61·7 44·3 56·5 44·3 60·1 46·6 44·9 52·3 50·1 56·6 45·2 45·5 46·6 46·1 55·3 34·7 8·4 7·4 3·1 5·5 1·3 10·4 0·5 0·2 0·7 0·4 4·0 10·4 3·7 4·8 5·2 6·7 9·7 3·8 5·8 8·1 5·4 2·4 6·7 14·7 ·300 ·506 ·429 ·323 ·487 ·374 ·362 ·483 ·553 ·307 ·466 ·307 ·525 ·332 ·314 ·405 ·374 ·467 ·316 ·320 ·333 ·327 ·447 ·219 71·1 85·5 80·8 73·3 81·7 77·4 64·1 83·9 88·6 64·8 79·2 66·5 82·5 70·2 72·9 78·3 81·2 80·0 67·0 77·1 79·7 78·5 80·8 71·0 67·2 74·2 73·7 64·8 72·9 70·2 56·3 76·2 79·0 58·3 69·5 59·7 76·7 55·0 65·7 66·1 74·1 73·8 49·8 70·5 60·8 71·8 62·0 54·7 3·9 11·3 7·1 8·5 8·8 7·2 7·8 7·7 9·6 6·5 9·7 6·8 5·8 15·2 7·2 12·2 7·1 6·2 17·2 6·6 18·9 6·7 18·8 16·3 ·663 ·834 ·819 ·614 ·797 ·731 ·462 ·889 ·969 ·495 ·715 ·517 ·901 ·442 ·632 ·639 ·834 ·820 ·370 ·738 ·538 ·771 ·559 ·439

137 Mean 55·7 50·4 5·4 ·387 76·5 66·8 9·7 ·675

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·837 4·33 gr. 0·730 7·12 gr.

ELEVATION 5000 TO 6000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

4 4 2 7 5 3 4 6 8 8 7 6 8 5 6 3 8 6 3 4 6 16 2 4 3 3 3 3 2 3 3 22 21 20 21 21 Nampok Tengling Choongtam, sunrise Choongtam, 9.50 a.m. Choongtam, noon Choongtam, 2.45 p.m. Choongtam, 4 p.m. Choongtam, sunset Choongtam, 9.50 a.m. Choongtam, noon Choongtam, 2.40 p.m. Choongtam, 4 p.m. Choongtam, sunset Sulloobong Lingdam Makaroumbi Khabang Lingdam Yankutamg Namtchi Yoksun Ditto Loongtoon Sakkiazong Phadong, 8 a.m. Phadong, 9.50 a.m. Phadong, noon Phadong, 2.40 p.m. Phadong, 4 p.m. Phadong, sunset Tumloong Tumloong, 9. 50 a.m. Tumloong, noon Tumloong, 2.40 p.m. Tumloong, 4 p.m. Tumloong, sunset 5075 5257 5368 5368 5368 5368 5368 5368 5368 5368 5368 5368 5368 5277 5375 5485 5505 5554 5564 5608 5619 5619 5677 5625 5946 5946 5946 5946 5946 5946 5368 5976 5976 5976 5976 5976 May Jan. May May May May May May Aug. Aug. Aug. Aug. Aug. Nov. Dec. Nov. Dec. Dec. Dec. May Jan. Jan. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov. Nov/Dec. Nov/Dec. Nov/Dec. Nov/Dec. Nov/Dec. 65·8 44·7 54·9 71·5 71·0 66·4 63·5 61·4 76·3 78·8 72·9 69·5 66·9 57·6 44·3 52·1 55·1 45·0 43·6 67·1 42·7 43·0 45·3 54·1 51·9 55·9 60·7 57·4 55·5 53·7 64·2 54·1 57·3 57·3 54·7 51·8 60·8 39·1 54·7 58·9 59·4 59·4 59·2 60·5 66·1 67·8 66·5 66·8 65·4 51·2 43·0 48·1 47·3 43·7 41·7 61·2 34·0 33·9 42·8 50·9 50·8 53·0 56·5 54·7 52·8 52·6 62·6 50·0 51·7 51·4 50·5 48·5 5·0 5·6 0·2 12·6 11·6 7·0 4·3 0·9 10·2 11·0 6·4 2·7 1·5 6·4 1·3 4·0 7·8 1·3 1·9 5·9 8·7 9·1 2·5 3·2 1·1 2·9 4·2 2·7 2·7 1·1 1·6 4·1 5·6 5·9 4·2 3·3 ·537 ·257 ·438 ·504 ·513 ·513 ·510 ·532 ·640 ·677 ·649 ·655 ·627 ·390 ·293 ·350 ·340 ·301 ·280 ·544 ·214 ·213 ·292 ·358 ·383 ·413 ·465 ·438 ·410 ·408 ·570 ·375 ·396 ·391 ·380 ·355 83·1 65·4 78·2 89·8 92·7 95·4 93·6 89·1 85·3 86·6 86·4 85·3 83·6 79·4 68·8 72·5 75·0 71·0 69·5 87·7 68·2 66·2 72·1 78·3 75·0 80·9 85·6 86·6 85·5 80·6 83·8 75·1 79·7 81·3 80·2 76·7 74·7 38·1 73·9 80·0 79·9 78·7 79·0 77·1 78·9 78·8 78·8 79·3 78·5 65·8 59·9 60·5 64·7 56·5 63·1 74·9 58·1 51·9 63·8 66·1 67·5 67·9 64·8 62·2 61·9 67·4 77·5 61·9 60·1 58·0 58·6 61·2 8·4 27·3 4·3 9·8 12·8 16·7 14·6 12·0 6·4 7·8 7·6 6·0 5·1 13·6 8·9 12·0 10·3 14·5 6·4 12·8 10·1 14·3 8·3 12·2 7·5 13·0 20·8 24·4 23·6 13·2 6·3 13·2 19·6 23·3 21·6 15·5 ·845 ·247 ·826 1·000 ·999 ·959 ·971 ·915 ·967 ·965 ·963 ·980 ·956 ·634 ·521 ·532 ·611 ·466 ·579 ·850 ·492 ·399 ·595 ·639 ·670 ·678 ·613 ·562 ·557 ·667 ·924 ·557 ·524 ·489 ·499 ·545

260 Mean 57·7 53·3 4·5 ·438 77·6 67·8 9·8 ·700

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·865 4·70 gr. 0·730 7·34 gr.

ELEVATION 6000 TO 7000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

5 11 11 4 2 4 4 3 1 10 4 6 7 4 Runkpo Leebong Ditto Dholeep Iwa River Dengha Kulhait River Latong Doobdi Pemiongchi Keadom Hee-hill Dumpook Changachelling 6008 6021 6021 6133 6159 6368 6390 6391 6472 6584 6609 6677 6678 6828 Nov. Feb. Jan. May Dec. Aug. Dec. Oct. Jan. Jan. Aug. Jan. Jan. Jan. 57·5 47·8 47·8 60·5 41·2 66·7 41·9 54·0 46·6 40·7 63·5 40·8 40·2 50·6 54·8 43·7 43·4 59·9 40·5 64·0 41·9 53·2 36·2 35·8 60·0 34·1 31·8 31·8 2·7 4·1 4·4 0·6 0·7 2·7 0 0·8 10·4 4·9 3·5 6·7 8·4 18·8 ·440 ·300 ·297 ·520 ·269 ·597 ·283 ·416 ·231 ·228 ·523 ·215 ·198 ·198 79·5 74·9 66·9 89·4 69·6 86·1 71·3 55·5 78·7 66·3 79·7 64·0 68·5 68·3 73·4 59·7 56·2 81·4 60·2 78·8 60·9 44·1 58·0 54·4 77·5 58·0 53·8 53·6 6·1 15·2 10·7 8·0 9·4 7·3 10·4 11·4 20·7 11·9 2·2 6·0 14·7 14·8 ·810 ·517 ·460 ·046 ·527 ·962 ·539 ·305 ·490 ·434 ·925 ·489 ·426 ·423

76 Mean 50·0 45·1 4·9 ·337 72·8 62·1 10·6 ·597

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·845 3·60 gr. 0·701 6·11 gr.

ELEVATION 7000 TO 8000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

1 2 8 1 1 4 8 Pemiongchi Goong Kampo-Samdong Hee-hill Ratong river Source of Balasun Goong ridge 7083 7216 7329 7289 7143 7436 7441 Jan. Nov. May/Aug. Jan. Jan. Oct. Oct. 46·2 49·0 59·1 51·3 36·5 48·3 51·2 33·5 48·5 58·2 26·4 25·3 48·3 50·2 12·7 0·5 0·9 24·9 11·2 0 1·0 ·210 ·355 ·493 ·163 ·157 ·352 ·376 76·8 79·7 83·6 72·8 60·0 81·2 80·7 51·8 69·1 77·4 56·6 52·9 73·7 66·9 25·0 10·6 6·2 16·2 7·1 7·5 13·8 ·396 ·705 ·922 ·466 ·412 ·819 ·657

35 Dorjiling Mean 48·8 41·5 7·3 ·301 76·4 64·1 12·8 ·625

From mean of above and Dorjiling Calcutta

Humidity Weight of vapour 0·826 3·85 gr. 0·668 7·28 gr.

ELEVATION 8000 TO 9000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

4 2 1 2 3 4 6 9 1 11 12 7 4 7 10 12 10 10 4 5 6 8 11 11 7 6 8 10 1 1 Sinchul Sinchul Ascent of Tonglo Tambur river Sakkiazong Chateng Buckim Buckim Chateng Lachoong, 7 a.m. Lachoong, 9.50 a.m. Lachoong, noon Lachoong, 2.40 p.m. Lachoong, 4 p.m. Lachoong, sunset Lachoong, Miscellaneous Lamteng, 6 a.m. Lamteng, 9.50 a.m. Lamteng, noon Lamteng, 2.40 p.m. Lamteng, 4 p.m. Lamteng, sunset Zemu Samdong, 7 a.m. Zemu Samdong, 9.50 a.m. Zemu Samdong, noon Zemu Samdong, 2.40 p.m. Zemu Samdong, sunset Zemu Samdong, 4 p.m. Goong Tendong (top) 8607 8607 8148 8081 8353 8418 8659 8659 8752 8777 8777 8777 8777 8777 8777 8777 8884 8884 8884 8884 8884 8884 8976 8976 8976 8976 8976 8976 8999 8663 Jan. Apr. May Nov. Nov. Oct. Jan. Jan. May | | | Aug. | and | Oct. | | | May, | June, | July | and | Aug. | | | June | and | July | | Nov. May 41·7 66·8 56·2 38·0 49·7 43·8 30·2 33·9 67·2 53·3 60·2 61·6 58·1 58·6 55·5 55·9 53·9 62·8 62·8 58·3 56·2 53·3 55·7 59·7 63·1 61·0 57·9 53·8 49·0 55·5 34·3 44·6 54·4 33·9 37·4 43·2 22·8 33·1 60·7 51·1 55·3 57·1 56·4 53·8 54·3 49·6 52·0 56·2 56·2 54·4 54·7 52·5 55·3 52·8 57·1 58·6 56·1 52·6 48·5 50·0 7·4 22·2 1·8 4·1 12·3 0·6 7·4 0·8 6·5 2·2 4·9 4·5 1·7 4·8 1·2 6·3 1·9 6·6 6·6 3·9 1·5 0·8 0·4 6·9 6·0 2·4 1·8 1·2 0·5 5·5 ·216 ·310 ·434 ·213 ·241 ·299 ·143 ·207 ·536 ·388 ·447 ·475 ·464 ·424 ·432 ·368 ·400 ·461 ·461 ·435 ·438 ·407 ·448 ·412 ·473 ·500 ·459 ·407 ·355 ·373 66·3 96·9 86·8 71·7 74·0 79·2 68·6 69·8 89·7 83·0 87·1 90·1 88·0 87·5 84·5 85·9 59·5 88·3 92·0 92·2 92·3 88·1 80·4 86·3 88·0 89·6 89·3 82·7 79·7 88·6 56·9 75·4 78·9 64·1 62·4 77·5 49·4 52·2 76·8 78·9 79·9 79·4 80·0 79·4 78·7 75·2 56·4 78·7 78·0 78·4 77·1 77·4 79·8 79·0 79·8 78·2 79·0 77·3 69·1 78·1 9·4 21·5 7·9 7·6 11·6 1·7 19·2 17·6 12·9 4·1 7·2 10·7 8·0 8·1 5·8 10·7 3·1 9·6 14·0 13·8 15·2 10·7 0·6 7·3 8·2 11·4 10·3 5·4 10·6 10·5 ·472 ·866 ·967 ·599 ·566 ·926 ·366 ·403 ·904 ·967 ·999 ·983 1·007 ·981 ·959 ·858 ·464 ·959 ·939 ·950 ·914 ·922 ·997 ·969 ·994 ·944 ·970 ·920 ·705 ·943

193 Mean 54·5 50·0 4·5 ·388 83·7 73·7 9·8 ·847

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·858 4·23 gr. 0·730 8·75 gr.

ELEVATION 9000 TO 10,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

4 8 4 1 1 Yangma Guola Nanki Singalelah Sakkiazong Zemu river 9279 9320 9295 9322 9828 Nov. Nov. Dec. Nov. June 37·8 42·3 36·2 53·5 60·0 33·1 38·3 35·7 33·3 47·6 4·7 4·0 0·5 20·2 12·4 ·207 ·249 ·227 ·209 ·343 72·7 52·2 70·9 80·0 93·3 61·4 48·3 62·1 57·3 81·9 11·3 3·9 8·8 22·7 11·4 ·549 ·352 ·560 ·478 1·062

18 Mean 46·0 37·6 8·4 ·247 73·8 62·2 11·6 ·600

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·747 2·80 gr. 0·724 6·28 gr.

ELEVATION 10,000 TO 11,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

13 5 4 2 2 4 10 4 3 16 17 9 8 9 15 4 Tonglo Nanki Yalloong river Tonglo top Yeunga Zemu river Wallanchoon Laghep Laghep Thlonok river, 7 a.m. Thlonok river, 9.50 a.m. Thlonok river, noon Thlonok river, 2.40 p.m. Thlonok river, 4 p.m. Thlonok river, sunset Yangma Valley 10,008 10,024 10,058 10,079 10,196 10,247 10,384 10,423 10,423 10,486 10,486 10,486 10,486 10,486 10,486 10,999 May Nov. Dec. May Oct. June Nov. Nov. Nov. June June June June June June Dec. 51·5 42·8 37·7 49·9 45·9 45·4 37·9 46·0 37·6 48·5 57·6 56·1 54·8 53·4 49·8 31·6 50·2 35·5 29·6 47·9 44·7 44·2 30·2 42·4 37·0 47·2 51·4 50·6 50·6 50·6 48·9 24·3 1·3 7·3 8·1 2·0 1·2 1·2 7·7 3·6 0·6 1·3 6·2 5·5 4·2 2·8 0·9 7·3 ·376 ·225 ·183 ·348 ·311 ·306 ·187 ·287 ·238 ·339 ·392 ·382 ·381 ·381 ·359 ·149 88·8 79·5 77·7 89·4 79·5 84·6 76·5 80·9 75·3 79·0 87·4 90·0 88·5 88·7 85·5 74·4 80·8 65·8 62·1 80·5 77·1 75·1 61·9 68·0 69·4 75·1 78·8 79·3 79·7 78·7 78·0 61·9 8·0 13·7 15·6 8·9 2·4 9·5 14·6 12·9 5·9 3·9 8·6 10·7 8·8 10·0 7·5 12·3 1·030 ·633 ·560 1·018 ·915 ·856 ·558 ·681 ·712 ·856 ·965 ·979 ·991 ·962 ·938 ·558

123 Mean 46·7 42·8 3·8 ·303 82·8 73·3 9·5 ·826

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·878 3·35 gr. 0·740 8·70 gr.

ELEVATION 11,000 TO 12,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

3 3 1 12 6 8 5 6 6 2 10 9 5 7 4 10 7 Barfonchen Punying Kambachen village Tallum, 7 a.m. Tallum, 9.50 a.m. Tallum, noon Tallum, 2.40 p.m. Tallum, 4 p.m. Tallum, sunset Kambachen Valley Yeumtong, 7 a.m. Yeumtong, 9.50 a.m. Yeumtong, noon Yeumtong 2.40 p.m. Yeumtong, 4 p.m. Yeumtong, sunset Yeumtong, Miscellaneous 11,233 11,299 11,378 11,482 11,482 11,482 11,482 11,482 11,482 11,484 11,887 11,887 11,887 11,887 11,887 11,887 11,887 Nov. Aug. Dec. July July July July July July Dec. | | Aug., | Sep., | and | Oct. | Oct. 36·8 50·2 43·3 50·4 58·1 57·9 55·7 54·3 48·8 30·4 44·4 53·6 54·5 48·8 48·4 42·0 43·5 31·9 49·5 32·5 47·8 50·5 50·8 50·2 50·1 47·3 26·0 43·8 48·9 48·3 47·4 47·1 35·9 37·1 4·9 0·7 10·8 2·6 7·6 7·1 5·5 4·2 1·5 4·4 0·6 4·7 6·2 1·4 1·3 6·1 6·4 ·198 ·367 ·203 ·347 ·380 ·384 ·377 ·375 ·340 ·161 ·302 ·360 ·353 ·342 ·338 ·229 ·239 76·3 84·5 80·0 85·0 88·1 89·7 89·3 90·3 86·6 69·9 83·0 87·5 89·7 87·2 85·2 60·6 83·7 69·6 78·8 61·2 80·3 79·7 81·3 80·6 79·4 80·0 59·5 78·9 78·7 77·2 77·2 77·8 58·5 69·7 6·7 5·7 18·8 4·7 8·4 8·4 8·7 10·9 6·6 10·4 4·1 8·8 12·5 10·0 7·4 2·1 14·0 ·719 ·963 ·544 1·010 ·993 1·043 1·020 ·981 1·001 ·515 ·967 ·959 ·917 ·915 ·934 ·497 ·720

104 Mean 48·3 43·8 4·5 ·311 83·3 74·6 8·7 ·865

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·860 3·46 gr. 0·760 9·00 gr.

ELEVATION 12,000 TO 13,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

9 9 7 7 7 8 2 1 3 7 5 1 1 6 3 4 4 4 4 6 23 13 6 Zemu river, 7 a.m. Zemu river, 9.50 a.m. Zemu river, noon Zemu river, 2.40 p.m. Zemu river, 4 p.m. Zemu river, sunset Tangma Valley Zemu river Chumanako Tungu, 7 a.m. Tungu, 9.50 a.m. Tungu, noon Tungu, 2.40 p.m. Tungu, sunset Tungu, sunrise Tungu, 9.50 a.m. Tungu, noon Tungu, 2.40 p.m. Tungu, 4 p.m. Tungu, sunset Tungu, Miscellaneous Tungu, Miscellaneous Tuquoroma 12,070 12,070 12,070 12,070 12,070 12,070 12,129 12,422 12,590 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,751 12,994 | | June | and | July | | Nov. June Nov. July July July July July Oct. Oct. Oct. Oct. Oct. Oct. Oct. July Nov. 46·6 51·1 51·1 51·2 49·7 48·1 34·8 49·0 37·3 45·1 53·1 62·3 60·0 46·4 38·2 46·5 46·1 43·8 42·3 41·0 43·2 51·3 26·0 45·6 49·0 50·2 50·3 48·9 47·6 22·7 46·6 28·3 44·1 48·6 52·7 53·8 45·3 35·0 42·8 42·0 42·1 40·8 38·7 40·8 47·7 23·4 1·0 2·1 0·9 0·9 0·8 0·5 12·1 2·4 9·0 1·0 4·5 9·6 6·2 1·1 3·2 3·7 4·1 1·7 1·5 2·3 2·4 3·6 2·6 ·321 ·362 ·376 ·377 ·360 ·344 ·143 ·332 ·174 ·305 ·355 ·409 ·425 ·317 ·222 ·292 ·284 ·285 ·271 ·253 ·272 ·345 ·146 80·6 84·5 87·0 86·3 86·5 81·4 70·6 93·2 75·1 80·5 87·1 88·9 85·3 84·7 79·4 85·0 85·0 86·4 85·9 83·3 84·5 85·7 75·1 77·7 75·1 82·2 80·0 80·2 77·5 63·7 79·6 73·8 78·3 79·4 77·8 79·5 79·1 77·8 78·6 78·2 78·8 78·5 78·2 78·4 79·0 60·8 2·9 9·4 4·8 6·3 6·3 3·9 6·9 13·6 1·3 2·2 7·7 11·1 5·8 5·6 1·6 6·4 6·8 7·6 7·4 5·1 6·1 6·7 14·3 ·931 ·972 1·074 1·000 1·006 ·926 ·592 ·989 ·822 ·949 ·982 ·935 ·985 ·974 ·932 ·957 ·944 ·963 ·956 ·947 ·950 ·971 ·537

140 Mean 46·3 42·9 3·4 ·303 83·6 77·1 6·5 ·926

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·890 3·37 gr. 0·815 9·75 gr.

ELEVATION 13,000 TO 14,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

7 4 2 21 1 4 10 1 3 Mon Lepcha Mon Lepcha Tunkra valley Jongri Zemu river Choonjerma Yangma village Wallanchoon road Kambachen, below pass 13,090 13,073 13,111 13,194 13,281 13,288 13,502 13,505 13,600 Jan. Jan. Aug. Jan. June Dec. Nov./Dec. Nov. Dec. 27·1 25·6 45·0 22·7 46·7 39·0 33·8 28·0 40·0 18·5 16·4 43·5 10·5 46·7 11·1 18·6 9·5 18·6 8·6 9·2 1·5 12·2 0 27·9 15·2 18·5 21·4 ·122 ·113 ·298 ·091 ·334 ·093 ·123 ·088 ·123 70·0 71·7 81·2 70·6 92·9 69·8 78·9 66·4 72·9 50·8 49·4 78·7 53·2 86·6 61·8 62·1 61·8 62·2 19·2 21·8 2·5 17·4 6·2 8·0 16·8 4·6 10·7 ·527 ·373 ·962 ·417 1·230 ·555 ·561 ·555 ·563

53 Mean 34·2 21·5 12·6 ·154 74·9 63·0 11·9 ·636

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·634 1·61 gr. 0·678 6·28 gr.

ELEVATION 15,000 TO 16,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

1 1 8 12 6 4 8 10 16 8 6 3 2 1 1 Yangma valley Choonjerma pass Lachee-pia Momay, 7 a.m. Momay, 9.50 a.m. Momay, noon Momay, 2.40 p.m. Momay, 4 p.m. Momay, sunset Momay, Miscellaneous Momay, Miscellaneous Sittong Palung Kambachen pass Yeumtong 15,186 15,259 15,262 15,262 15,262 15,262 15,262 15,262 15,262 15,262 15,262 15,372 15,676 15,770 15,985 Dec. Dec. Aug. Sept. Sept. Sept. Sept. Sept. Sept. Sept. Oct. Oct. Oct. Dec. Sept. 42·2 34·3 42·0 39·4 50·9 51·7 49·7 44·4 41·5 47·6 40·9 38·6 44·6 26·5 44·6 20·7 10·5 41·6 34·7 41·7 43·6 41·9 41·3 38·6 41·4 36·5 29·8 39·8 15·9 43·7 21·5 23·8 0·4 4·7 9·2 8·1 7·8 3·1 2·9 6·2 4·4 8·8 4·8 10·6 0·9 ·133 ·091 ·279 ·219 ·280 ·299 ·283 ·276 ·252 ·277 ·234 ·184 ·262 ·111 ·300 80·8 77·9 85·5 80·5 87·6 89·5 90·0 88·7 84·2 87·4 83·9 84·0 86·8 78·0 88·8 62·0 60·6 79·4 78·8 78·8 79·7 78·3 77·6 78·4 78·6 69·3 77·5 78·5 58·5 80·5 18·8 17·3 6·1 1·7 8·8 9·8 11·7 11·1 5·8 8·8 14·6 6·5 8·3 19·5 8·3 ·559 ·534 ·982 ·966 ·963 ·990 ·949 ·928 ·952 ·956 ·710 ·926 ·954 ·498 1·016

87 Mean 42·6 34·8 7·8 ·232 84·9 74·4 10·5 ·859

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·763 2·55 gr. 0·719 8·95 gr.

ELEVATION 16,000 TO 17,000 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

1 3 1 5 6 1 Kanglachem pass Tunkra pass Wallanchoon pass Yeumtso Cholamoo lake Donkia mountain 16,038 16,083 16,756 16,808 16,900 16,978 Dec. Aug. Nov. Oct. Oct. Sept. 32·8 39·8 18·0 32·4 31·4 40·2 16·3 38·7 –6·0 25·1 20·2 25·9 16·5 1·1 24·0 7·3 11·2 14·3 ·110 ·252 ·046 ·156 ·130 ·160 80·7 86·0 79·9 85·0 79·8 87·6 61·1 78·7 57·6 75·7 68·4 78·8 19·6 7·3 22·3 9·3 11·4 8·8 ·543 ·959 ·483 ·872 ·690 ·963

17 Mean 32·4 20·0 12·4 ·142 83·2 70·1 13·3 ·752

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·640 1·53 gr. 0·658 7·80 gr.

ELEVATION 17,000 TO 18,500 FEET

EAST NEPAL AND SIKKIM CALCUTTA

No. of Obs. Locality Elev. Month Temp. Dew Point Diff. Tens. Temp. Dew Point Diff. Tens.

1 1 1 3 2 2 Kinchinjhow Sebolah pass Donkia mountain Bhomtso Donkia pass Donkia pass 17,624 17,585 18,307 18,450 18,466 18,466 Sept. Sept. Sept. Oct. Sept. Oct. 47·5 46·5 38·8 54·0 41·8 40·1 30·9 34·6 35·3 4·4 30·3 25·0 16·6 11·9 3·5 49·6 11·5 15·1 ·191 ·218 ·224 ·072 ·188 ·155 85·7 88·8 90·7 91·1 84·1 86·5 79·7 80·0 79·3 61·1 78·4 65·5 6·0 8·8 11·4 20·0 5·7 21·0 ·991 1·002 ·981 ·543 ·950 ·627

10 Mean 44·8 26·8 18·0 ·175 87·8 74·0 12·2 ·849

East Nepal and Sikkim Calcutta

Humidity Weight of vapour 0·532 1·90 gr. 0·648 8·78 gr.

SUMMARY

HUMIDITY WEIGHT OF VAPOUR

No. of Obs. Elevations in Feet Stations Sikkim Calcutta Diff. Sikkim Sikkim Calcutta Diff. Sikkim

48 49 48 137 260 76 1023 193 18 123 104 140 53 87 17 10 735 to 2000 2000 to 3000 3000 to 4000 4000 to 5000 5000 to 6000 6000 to 7000 7000 to 8000 8000 to 9000 9000 to 10,000 10,000 to 11,000 11,000 to 12,000 12,000 to 13,000 13,000 to 14,000 15,000 to 16,000 16,000 to 17,000 17,000 to 18,000 9 9 13 23 15 13 14 13 5 10 6 6 9 8 6 5 ·717 ·820 ·858 ·837 ·865 ·845 ·826 ·858 ·747 ·878 ·860 ·890 ·634 ·763 ·640 ·532 ·663 ·740 ·732 ·730 ·730 ·701 ·668 ·730 ·724 ·740 ·760 ·815 ·678 ·719 ·658 ·648 +·054 ·080 ·116 ·107 ·135 ·144 ·158 ·128 ·023 ·138 ·100 ·075 –·044 +·044 ·018 –·116 5·57 5·45 4·23 4·33 4·70 3·60 3·85 4·23 2·80 3·35 3·46 3·37 1·61 2·55 1·53 1·90 6·88 7·13 6·60 7·12 7·34 6·71 7·28 8·75 6·28 8·70 9·00 9·75 6·28 8·95 7·80 8·78 –1·31 1·68 2·37 2·79 2·64 3·11 3·43 4·52 3·48 4·35 5·54 6·38 4·67 6·40 6·27 6·88

2386 154

Considering how desultory the observations in Sikkim are, and how much affected by local circumstances, the above results must be considered highly satisfactory: they prove that the relative humidity of the atmospheric column remains pretty constant throughout all elevations, except when these are in a Tibetan climate; and when above 18,000 feet, elevations which I attained in fine weather only. Up to 12,000 feet this constant humidity is very marked; the observations made at greater elevations were almost invariably to the north, or leeward of the great snowy peaks, and consequently in a drier climate; and there it will be seen that these proportions are occasionally inverted; and in Tibet itself a degree of relative dryness is encountered, such as is never equalled on the plains of Eastern Bengal or the Gangetic delta. Whether an isolated peak rising near Calcutta, to the elevation of 19,000 feet, would present similar results to the above, is not proven by these observations, but as the relative humidity is the same at all elevations on the outermost ranges of Sikkim, which attain 10,000 feet, and as these rise from the plains like steep islands out of the ocean, it may be presumed that the effects of elevation would be the same in both cases.

The first effect of this humid wind is to clothe Sikkim with forests, that make it moister still; and however difficult it is to separate cause from effect in such cases as those of the reciprocal action of humidity on vegetation, and vegetation on humidity, it is necessary for the observer to consider the one as the effect of the other. There is no doubt that but for the humidity of the region, the Sikkim Himalaya would not present the uniform clothing of forest that it does; and, on the other hand, that but for this vegetation, the relative humidity would not be so great.^[433]

The great amount of relative humidity registered at 6000 to 8000 feet, arises from most of the observations having been made on the outer range, where the atmosphere is surcharged. The majority of those at 10,000 to 12,000 feet, which also give a disproportionate amount of humidity, were registered at the Zemu and Thlonok rivers, where the narrowness of the valleys, the proximity of great snowy peaks, and the rank luxuriance of the vegetation, all favour a humid atmosphere.

I would have added the relative rain-fall to the above, but this is so very local a phenomenon, and my observations were so repeatedly deranged by having to camp in forests, and by local obstacles of all kinds, that I have suppressed them; their general results I have given in Appendix F.

I here add a few observations, taken on the plains at the foot of the Sikkim Himalaya during the spring months.

Comparison between Temperature and Humidity of the Sikkim Terai and Calcutta, in March and April, 1849.

No. of Obs. Locality Elev. above sea. Feet TEMPERATURE DEW POINT TENSION SAT.

C. T. C. T. C. T. C. T.

4 4 3 3 4 3 2 8 Rummai Belakoba Rangamally Bhojepore Thakyagunj Bhatgong Sahibgunj Titalya 293 368 275 404 284 225 231 362 82·2 92·8 84·2 90·1 84·9 87·4 80·2 85·5 70·6 85·5 75·0 81·2 77·1 74·9 68·0 80·0 61·7 62·6 68·7 54·1 61·3 64·7 66·2 55·4 60·5 63·0 62·5 44·3 60·8 54·6 53·1 56·1 ·553 ·570 ·695 ·429 ·547 ·611 ·642 ·448 ·532 ·578 ·568 ·308 ·537 ·436 ·414 ·459 ·517 ·382 ·605 ·313 ·466 ·480 ·635 ·376 ·717 ·485 ·665 ·295 ·588 ·512 ·409 ·459

31 Means 305 85·9 79·0 61·8 56·9 ·562 ·479 ·472 ·516

May, 1850 Kishengunj 131 89·7 K 78·6 76·7 K 71·4 ·904 K ·759 ·665 K ·793

Vapour in a cubic foot

Kishengunj Calcutta 8·20 9·52 Terai Calcutta 5·08 5·90

Mean difference of temperature between Terai and Calcutta, from 31 observations in March, as above, excluding mimima, Terai Mean difference from 26 observations in March, including mimima, Terai Mean difference of temperature at Siligoree on May 1, 1850 Mean difference of temperature at Kishengunj on May 1, 1850 6·9 9·7 10·9 11·1

From the above, it appears that during the spring months, and before the rains commence, the belt of sandy and grassy land along the Himalaya, though only 3·5° north of Calcutta, is at least 6° or 7° colder, and always more humid relatively, though there is absolutely less moisture suspended in the air. After the rains commence; I believe that this is in a great measure inverted, the plains becoming excessively heated, and the temperature being higher than at Calcutta. This indeed follows from the well known fact that the summer heat increases greatly in advancing north-west from the Bay of Bengal to the trans-Sutledge regions; it is admirably expressed in the maps of Dove’s great work “On the Distribution of Heat on the Surface of the Globe.”

H. ON THE TEMPERATURE OF THE SOIL AT VARIOUS ELEVATIONS.

These observations were taken by burying a brass tube two feet six inches to three feet deep, in exposed soil, and sinking in it, by a string or tied to a slip of wood, a thermometer whose bulb was well padded with wool: this, after a few hours’ rest, indicates the temperature of the soil. Such a tube and thermometer I usually caused to be sunk wherever I halted, if even for one night, except during the height of the rains, which are so heavy that they communicate to the earth a temperature considerably above that of the air.

The results proved that the temperature of the soil at Dorjiling varies with that of the month, from 46° to 62·2°, but is hardly affected by the diurnal variation, except in extreme cases. In summer, throughout the rains, May to October, the temperature is that of the month, which is imparted by the rain to the depth of eleven feet during heavy continued falls (of six to twelve inches a day), on which occasions I have seen the buried thermometer indicating a temperature above the mean of the month. Again, in the winter months, December and January, it stands 5° above the monthly mean; in November and February 4° to 5°; in March a few degrees below the mean temperature of the month, and in October above it; April and May being sunny, it stands above their mean; June to September a little below the mean temperature of each respectively.

The temperature of the soil is affected by:—1. The exposure of the surface; 2. The nature of the soil; 3. Its permeability by rain, and the presence of underground springs; 4. The sun’s declination; 5. The elevation above the sea, and consequently the heating power of the sun’s rays: and 6, The amount of cloud and sunshine. far from being sufficient to supply data for the exact estimation of the effects of the sun on the soil at any elevation or locality; they, however, indicate with tolerable certainty the main features of this phenomenon, and these are in entire conformity with more ample series obtained elsewhere. The result, which at first sight appears the most anomalous, is, that the mean temperature of the soil, at two or three feet depth, is almost throughout the year in India above that of the surrounding atmosphere. This has been also ascertained to be the case in England by several observers, and the carefully conducted observations of Mr. Robert Thompson at the Horticultural Society’s Gardens at Chiswick, show that the temperature of the soil at that place is, on the mean of six years, at the depth of one foot, 1° above that of the air, and at two feet 1·5°. During the winter months the soil is considerably (l° to 3°) warmer than the air, and during summer the soil is a fraction of a degree cooler than the air.

In India, the sun’s declination being greater, these effects are much exaggerated, the soil on the plains being in winter sometimes 9° hotter than the air; and at considerable elevations in the Himalaya very much more than that; in summer also, the temperature of the soil seldom falls below that of the air, except where copious rain-falls communicate a low temperature, or where forests interfere with the sun’s rays.

At considerable elevations these effects are so greatly increased, that it is extremely probable that at certain localities the mean temperature of the soil may be even 10° warmer than that of the air; thus, at Jongri, elevation 13,194 feet, the soil in January was 34·5°, or 19·2° above the mean temperature of the month, immediately before the ground became covered with snow for the remainder of the winter; during the three succeeding months, therefore, the temperature of the soil probably does not fall below that of the snow, whilst the mean temperature of the air in January may be estimated at about 20°, February 22°, March 30°, and April 35°. If, again, we assume the temperature of the soil of Jongri to be that of other Sikkim localities between 10,000 and 14,000 feet, we may assume the soil to be warmer by 10° in July (see Tungu observations), by 8° or 9° in September (see Yeumtong); by l0° in October (see Tungu); and by 7° to l0° in November (see Wallanchoon and Nanki). These temperatures, however, vary extremely according to exposure and amount of sunshine; and I should expect that the greatest differences would be found in the sunny climate of Tibet, where the sun’s heat is most powerful. Were nocturnal or terrestrial radiation as constant and powerful as solar, the effects of the latter would be neutralised; but such is not the case at any elevation in Sikkim.

This accumulated heat in the upper strata of soil must have a very powerful effect upon vegetation, preventing the delicate rootlets of shrubs from becoming frozen, and preserving vitality in the more fleshy, roots, such as those of the large rhubarbs and small orchids, whose spongy cellular tissues would no doubt be ruptured by severe frosts. To the burrowing rodents, the hares, marmots, and rats, which abound at 15,000 to 17,000 feet in Tibet, this phenomenon is even more conspicuously important; for were the soil in winter to acquire the mean temperature of the air, it would take very long to heat after the melting of the snow, and indeed the latter phenomenon would be greatly retarded. The rapid development of vegetation after the disappearance of the snow, is no doubt also proximately due to the heat of the soil, quite as much as to the increased strength of the sun’s direct rays in lofty regions.

I have given in the column following that containing the temperature of the sunk thermometer, first the extreme temperatures of the air recorded during the time the instrument was sunk; and in the next following, the mean temperature of the air during the same period, so far as I could ascertain it from my own observations.

SERIES I. Soane Valley

Locality Date Eleva- tion (feet) Depth (ft. in.) Temperature of sunk Thermometer Extreme Temperature of Air observed Approx. Mean Temp. of Air deduced Diff. between Air and sunk Therm.

Muddunpore Nourunga Baroon Tilotho Akbarpore Feb. 11 to 12 Feb. 12 to 13 Feb. 13 to 14 Feb. 15 to 16 Feb. 17 to 19 440 340 345 395 400 3 4 3 8 2 4 4 6 (2 ther.) 4 6 5 6 71·5 71·7 68·5 76·5 76·0 62·0 to 77·5 57·0 to 71·0 53·5 to 76·0 58·5 to 80·0 56·9 to 79·5 67·0 67·3 67·6 67·8 68·0 +4·5 3·4 1·9 8·7 8·0

SERIES II. Himalaya of East Nepal and Sikkim

Locality Date Eleva- tion (feet) Depth (ft. in.) Temperature of sunk Thermometer Extreme Temperature of Air observed Approx. Mean Temp. of Air deduced Diff. between Air and sunk Therm.

Base of Tonglo Simsibong Tonglo saddle Tonglo summit Simonbong Nanki Sakkiazong Mywa guola Banks of Tambur higher up river Wallanchoon Yangma village Yangma river Bhomsong Tchonpong Jongri Buckeem Choongtam Junction of Thlonok and Zemu Tungu Tungu Lamteng Choongtam Lachoong Yeumtong Momay Yeumtso Lachoong Great Rungeet Leebong Kursiong Leebong Punkabaree Jillapahar (Mr. Hodgson’s) Superintendent’s house May 19 May 20 May 21 to 22 May 23 May 24 Nov. 4 to 5 Nov. 9 to 10 Nov. 17 to 18 Nov. 18 to 19 Nov. 19 to 20 Nov. 23 to 25 Nov. 30 to Dec. 3 Dec. 2 to 3 Dec. 24 to 25 Jan. 4 Jan. 10 to 11 Jan.12 May 19 to 25 June 13 to 16 July 26 to 30 Oct. 10 to 15 Aug. 1 to 3 Aug. 13 to 15 Aug. 17 to 19 Sept. 2 to 8 Sept. 10 to 14 Oct. 16 to 18 Oct. 24 to 25 Feb. 11 to 13 Feb. 14 to 15 Apr. 16 Apr. 22 May 1 | Aug. 15 to 16 | Aug. 15 to 16 | Aug. 20 to 22 | Aug. 20 to 22 | Sept. 9 | Sept. 9 | Oct. 6 | Oct. 20 | Feb. 18 to 28 | Mar. 1 to 13 | Apr. 18 to 20 | Apr. 30 Apr. 21 to 30 3,000 7,000 10,008 10,079 5,000 9,300 8,353 2,132 2,545 3,201 10,386 13,502 10,999 1,596 4,978 13,194 8,665 5,268 10,846 12,751 12,751 8,884 5,268 8,712 11,919 15,362 16,808 8,712 818 6,000 4,813 6,000 1,850 7,430 7,430 7,430 7,430 7,430 7,430 7,430 7,430 7,430 7,430 7,430 7,430 6,932 2 0 2 0 2 6 2 6 2 6 3 0 3 0 3 0 3 0 3 0 2 0 2 0 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 5 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 5 0 7 7 5 0 7 7 5 0 7 7 7 7 7 7 2 7 2 7 2 7 2 7 2 7 78 61·7 50·7^[434] 49·7 69·7 51·5 53·2 73·0 71·0 64·5 43·5 to 45·0 37·3 to 38·0 41·4 to 42·0 64·5 to 65·0 55·0 34·5 43·2 62·5 to 62·7 51·2 59·0 to 56·5 50·8 to 52·5 62·2 to 62·5 72·1 66·3 to 66·0 55·5 to 56·1 52·5 to 51·5 43·5 to 43·0 60·2 65·0 50·8 to 52·0 64·5 61·8 to 62·0 80·0 62·0 to 62·8 61·5 to 62·3 61·6 to 61·7 60·7 60·2 60·5 60·0 58·5 46·0 to 46·7 46·3 to 48·3 55·3 to 56·0 57·4 58·8 to 60·2 67·5 to 67·0 59·0 to 59·5 47·5 to 57·5 47·5 to 53·2 51·2 to 55·5 33·0 to 50·5 37·8 to 55·0 41·0 to 85·0 48·0 to 65·0 44·3 to 60·0 25·0 to 49·7 20·0 to 46·0 23·0 to 40·0 42·8 to 71·3 33·0 to 54·8 3·7 to 34·0 40·0 to 29·8 48·0 to 78·3 38·2 to 57·2 38·0 to 62·3 34·5 to 53·3 47·5 to 78·2 54·8 to 82·0 43·5 to 68·7 39·5 to 59·5 31·0 to 62·5 4·0 to 52·0 39·0 to 62·6 56·0 to 71·0 41·5 to 56·0 63·0 to 60·0 54·0 to 67·8 68·2 to 78·0 58·0 to 66·0 58·0 to 66·0 58·7 to 67·8 58·7 to 67·8 56·2 to 65·0 56·2 to 65·0 52·0 to 61·0 49·7 to 55·2 36·0 to 52·8 34·5 to 53·3 46·0 to 61·3 46·0 to 61·3 48·5 to 65·8 52·5 52·5 52·5 41·2 46·1 63·4 55·6 51·6 37·4 33·0 27·9 57·1 43·9 15·3 32·4 63·2 49·8 50·0 41·1 57·0 72·0 57·0 47·2 41·6 30·6 52·0 63·5 46·0 63·0 60·0 76·0 61·5 61·5 61·7 61·7 60·0 60·0 58·5 56·5 43·0 46·0 54·0 55·0 58·0 – 1·8 – 1·8 – 1·8 + 9·7 + 7·1 + 9·6 +15·4 +12·9 + 7·6 + 4·7 + 3·6 + 6·6 +11·1 +19·2 +10·8 – 0·6 + 1·4 + 7·7 +10·7 + 5·3 + 0·1 + 9·2 + 8·6 +10·4 +12·6 + 8·2 + 1·5 + 5·4 + 1·5 + 1·9 + 4·0 + 0·9 + 0·4 – 0·1 – 1·0 + 0·2 + 0·5 + 1·5 + 2·0 + 6·4 + 1·3 + 1·7 + 2·4 + 1·5

SERIES III. Plains of Bengal

Locality Date Eleva- tion (feet) Depth (ft. in.) Temperature of sunk Thermometer Extreme Temperature of Air observed Approx. Mean Temp. of Air deduced Diff. between Air and sunk Therm.

Kishengunj Dulalgunj Banks of Mahanuddy river Ditto Ditto Maldah Mahanuddy river Ganges Bauleah Dacca May 3 to 4 May 7 May 8 May 9 May 10 May 11 May 14 May 15 May 16 to 18 May 28 to 30 131 130 100 100 100 100 100 100 130 72 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 2 7 §82·8 to 83·0 §81·3 †79·3 †87·5 †88·0 †88·8 †87·8 †88·0 87·8 to 89·8 84·0 to 84·3 70·0 to 85·7 74·3 to 90·3 75·0 to 91·5 77·8 to 92·5 78·5 to 91·5 75·3 to 91·3 71·0 to 91·7 73·0 to 87·8 78·0 to 106·5 75·3 to 95·5 82·0 82·0 83·0 83·0 82·3 82·3 82·3 82·3 80·5 83·3 +0·8 –0·7 –3·7 –4·5 –5·7 –6·5 –4·5 –5·7 +7·3 +0·9

SERIES IV. Khasia Mountains

Locality Date Eleva- tion (feet) Depth (ft. in.) Temperature of sunk Thermometer Extreme Temperature of Air observed Approx. Mean Temp. of Air deduced Diff. between Air and sunk Therm.

Churra Churra Kala-panee Kala-panee Kala-panee Kala-panee Moflong Moflong Moflong Syong Syong Myrung Myrung Myrung Myrung Nunklow Nunklow Pomrang Pomrang June 28 to 25 Oct. 29 to Nov. 16 June 28 to 29 Aug. 5 to 7 Sept. 13 to 14 Oct. 27 to 28 June 30 to July 4 July 30 to Aug. 4 Oct. 25 to 27 July 29 to 30 Oct. 11 to 12 July 9 to 10 July 26 to 29 Oct. 12 to 17 Oct. 21 to 25 July 11 to 26 Oct. 17 to 21 Sept. 15 to 23 Oct. 6 to 10 4,226 5,302 6,062 5,725 5,647 4,688 5,143 2 7 2 7 2 7 2 7 2 7 2 7 2 7 *71·8 to 72·3 68·3 to 64·0 69·2 70·0 to 70·4 *70·2 *66·3 65·0 67·3 63·2 69·2 to 69·3 67·0 66·2 to 66·3 68·3 66·0 to 64·8 64·8 to 64·0 70·5 to 71·3 68·8 to 68·3 70·3 to 68·5 68·3 64·8 to 72·2 70·7 to 49·3 64·2 to 71·2 72·2 to 61·8 65·5 to 69·8 64·0 to 56·0 61·0 to 68·3 64·0 to 75·8 63·7 to 55·7 60·0 to 78·5 65·7 to 55·5 60·0 to 73·8 78·0 to 64·2 70·0 to 55·5 66·0 to 53·0 65·5 to 81·5 75·7 to 58·0 73·0 to 57·0 73·7 to 58·2 69·9 61·7 67·2 64·9 66·0 60·0 64·0 68·5 64·1 69·2 62·8 67·5 71·1 63·0 60·5 71·5 66·1 65·5 65·0 +2·2 +4·5 +2·0 +5·2 +4·2 +6·3 +2·2 –1·2 –0·9 +0·1 +4·2 –1·2 –2·8 +2·4 +3·9 –0·5 +2·5 +3·9 +3·3

SERIES V. Jheels, Gangetic Delta, and Chittagong

Locality Date Eleva- tion (feet) Depth (ft. in.) Temperature of sunk Thermometer Extreme Temperature of Air observed Approx. Mean Temp. of Air deduced Diff. between Air and sunk Therm.

Silchar Silhet Noacolly Chittagong Chittagong Chittagong, flagstaff hill Hat-hazaree Sidhee Hattiah Seetakoond Calcutta† Nov. 27 to 30 Dec. 3 to 7 Dec. 18 to 19 Dec. 23 to 31 Jan. 14 to 16 Dec. 28 to 30 Jan. 4 to 5 Jan. 5 to 6 Jan. 6 to 9 Jan. 9 to 14 Jan. 16 to Feb. 5 116 133 20 191 151 20 20 20 20 18 2 7 77·7 to 75·8 73·5 to 73·7 73·3 72·5 to 73·0 73·3 to 73·7 72·0 to 71·8 71·3 71·0 *67·7 73·3 to 73·7 76·0 to 77·0 55·0 to 81·7 63·0 to 74·5 58·5 to 76·5 53·2 to 75·0 61·3 to 78·7 55·2 to 74·2 50·5 to 62·0 52·7 to 70·2 50·2 to 77·5 55·2 to 79·5 §56·5 to 82·0 69·1 69·5 69·5 63·8 65·5 65·3 65·0 65·0 64·5 70·2 69·3 +7·7 +3·1 +3·8 +9·0 +8·3 +6·6 +6·3 +6·0 +3·2 +3·3 +7·2

I. ON THE DECREMENT OF TEMPERATURE IN ASCENDING THE SIKKIM HIMALAYA MOUNTAINS AND KHASIA MOUNTAINS

I have selected as many of my observations for temperature of the sir as appeared to be trustworthy, and which, also, were taken contemporaneously with others at Calcutta, and I have compared them with the Calcutta observations, in order to find the ratio of decrement of heat to an increase of elevation. The results of several sets of observations are grouped together, but show so great an amount of discrepancy, that it is evident that a long series of months and the selection of several stations are necessary in a mountain country to arrive at any accurate results. Even at the stations where the most numerous and the most trustworthy observations were recorded, the results of different months differ extremely; and with regard to the other stations, where few observations were taken, each one is affected differently from another at the same level with it, by the presence or proximity of forest, by exposure to the east or west, to ascending or descending currents in the valleys, and to cloud or sunshine. Other and still more important modifying influences are to be traced to the monthly variations in the amount of humidity in the air and the strength of its currents, to radiation, and to the evolution of heat which accompanies condensation raising the temperature of elevated regions during the rainy season. The proximity of large masses of snow has not the influence I should have expected in lowering the temperature of the surrounding atmosphere, partly no doubt because of the more rapid condensation of vapours which it effects, and partly because of the free circulation of the currents around it. The difference between the temperatures of adjacent grassy and naked or rocky spots, on the other hand, is very great indeed, the former soon becoming powerfully heated in lofty regions where the sun’s rays pass through a rarefied atmosphere, and the rocks especially radiating much of the heat thus accumulated, for long after sunset. In various parts of my journals I have alluded to other disturbing causes, which being all more or leas familiar to meteorologists, I need not recapitulate here. Their combined effects raise all the summer temperatures above what they should theoretically be.

In taking Calcutta as a standard of comparison, I have been guided by two circumstances; first, the necessity of selecting a spot where observations were regularly and accurately made; and secondly, the being able to satisfy myself by a comparison of my instruments that the results should be so far strictly comparable.

I have allowed 1° Fahr. for every degree in latitude intervening between Sikkim and Calcutta, as the probable ratio of diminution of temperature. So far as my observations made in east Bengal and in various parts of the Gangetic delta afford a means of solving this question, this is a near approximation to the truth. The spring observations however which I have made at the foot of the Sikkim Himalaya would indicate a much more rapid decrement; the mean temperature of Titalya and other parts of the plains south of the forests, between March and May being certainly 6°–9° lower than Calcutta: this period however is marked by north-west and north-east winds, and by a strong haze which prevents the sun’s rays from impinging on the soil with any effect. During the southerly winds, the same region is probably hotter than Calcutta, there being but scanty vegetation, and the rain-fall being moderate.

In the following observations solitary readings are always rejected.

I.—Summer or Rainy Season observations at Dorjiling.

Observations taken during the rainy season of 1848, at Mr. Hodgson’s (Jillapahar, Dorjiling) alt. 7,430 feet, exposure free to the north east and west, the slopes all round covered with heavy timber; much mist hence hangs over the station. The mean temperatures of the month at Jillapahar are deduced from horary observations, and those of Calcutta from the mean of the daily maximum and minimum.

Month No. of Obs. at Jillapahar Temp. Temp. Calcutta Equiv. of 1° Fahr.

July August September October 284 378 407 255 61·7 61·7 58·9 55·3 86·6 85·7 84·7 83·3 364 feet 346 feet 348 feet 316 feet

1,324 … Mean 344 feet

II.—Winter or dry season observations at Dorjiling.

1. Observations taken at Mr. J. Muller’s, and chiefly by himself, at “the Dale”; elev. 6,956 feet; a sheltered spot, with no forest near, and a free west exposure. 103 observations. Months: November, December, January, and February 1°=313 ft.

2. Observations at Dr. Campbell’s (Superintendent’s) house in April; elev. 6,950 feet; similar exposure to the last. 13 observations in April 1°=308 ft.

3. Observations by Mr. Muller at Colinton; elev. 7,179 feet; free exposure to north-west; much forest about the station, and a high ridge to east and south. 38 observations in winter months 1°=290 ft.

4. Miscellaneous (11) observations at Leebong; elev. 6000 feet; in February; free exposure all round 1°=266 ft.

5. Miscellaneous observations at “Smith’s Hotel;” Dorjiling, on a cleared ridge; exposed all round; elev. 6,863 feet. April and May 1°=252 ft. ————

Mean of winter observations Mean of summer observations Mean 1°=286 ft. 1°=344 ft. ———— 310 ft.

III.—Miscellaneous observations taken at different places in Dorjiling, elevations 6,900 to 7,400 feet, with the differences of temperature between Calcutta and Dorjiling.

Month Number of Observations Difference of Temperature Equivalent

January February March April March and April July August September October 27 84 37 7 29 83 74 95 18 30·4 32·8 41·9 36·0 37·3 23·6 22·4 25·7 29·5 1°=287 ft. 1°=265 ft. 1°=196 ft. 1°=236 ft. 1°=224 ft. 1°=389 ft. 1°=415 ft. 1°=350 ft. 1°=297 ft.

Sum 454 Mean 31·1 Mean 1°=295 ft.

These, it will be seen, give a result which approximates to that of the sets I and II. Being deduced from observations at different exposures, the effects of these may be supposed to be eliminated. It is to be observed that the probable results of the addition of November and December’s observations, would be balanced by those of May and June, which are hot moist months.