Note 26 — INTRODUCTION TO THE VOYAGE TO THE PACIFIC OCEAN.
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It must be observed, however, that Monsieur le Monier, in the Memoirs of the French Academy of Sciences for 1776, pleads for the existence of Cape Circumcision, seen by Bouvet in 1738, which our English navigator sought for in vain, and supposes to have been only an island of ice. Mr. Wales, in a paper read before the Royal Society, very forcibly replied to M. le Monier’s objections; and the attack having been repeated, he has drawn up a more extended defence of this part of Captain Cook’s Journal, which he hath very obligingly communicated, and is here inserted.
Arguments, tending to prove that Captain Cook sought for Cape Circumcision under the proper Meridian; and that the objections which have been made to his conduct, in this respect, are not well founded.
In the Memoirs of the Royal Academy of Sciences at Paris for 1776, printed in 1779, M. Le Monier has made some remarks with a design to show that Captain Cook sought the land, usually called Cape Circumcision, in a wrong place; and that, instead of looking for it under the meridian of 91⁄2° or 10° of east longitude, he ought to have looked for it under a meridian which is only 3°, or 31⁄2° to the eastward of the meridian of Greenwich; and consequently that this land may exist, notwithstanding all that has yet been done to find it. M. Le Monier has also two additional Memoirs on the same subject, in the volume for 1779, occasioned, as it appears, by some objections which have been made to his former Memoir before the Academy. For some reason or other, the Academy has not thought proper to print the objections which have been made to M. Le Monier’s hypothesis; nor has he been particular enough in his two Memoirs which reply to them, to enable me to say of what importance the objections are. I can only gather, that they contain some exceptions to the quantity by which M. Le Monier asserts the variation alters in 10° of longitude, under the parallel of 54° south; and which, I conceive, has little to do in the dispute.
Whether the land, usually called Cape Circumcision, exists or not, is a point of small importance to geography; as the most strenuous asserters of its existence must allow it to be a very inconsiderable island, and of no use. This, therefore, is not in itself a matter worthy of dispute; but in asserting this, M. Le Monier has, and I am sorry to observe it, with some asperity too, particularly in his second Memoir, endeavoured to censure the judgment and conduct of Captain Cook, whose memory I have every reason to revere, as well as the judgment of those who were with him; and, on this account, I cannot help feeling myself called on to explain the motives which induced Captain Cook to place no dependence on the arguments now adduced by M. Le Monier in support of his supposition; and which, M. Le Monier must know, were not unattended to at that time, from what the Captain has said, p. 236. Vol. II. of his account of the voyage. And it may be proper to observe here, that what fell from Captain Cook on this subject, was to show that this circumstance was then attended to, and not to throw blame on M. Bouvet, for whose memory and abilities Captain Cook entertained great respect: nor is it incompatible with the utmost respect, for a man to have a favourable opinion of his own labours; or to endeavour to show why he thinks the disagreement between them and those of another person, when there is one, does not arise from an error committed by himself. There could, therefore, be no occasion for M. Le Monier to express himself as he has done in several parts of his second Memoir.
The substance of M. Le Monier’s argument is this. In 1739, when M. Bouvet’s discovery is supposed to have been made, the methods for determining the longitude of a ship at sea were very defective; and, of course, the longitude of any land which happened accidentally to be seen by one, was equally uncertain. On a presumption that this was the case with respect to Cape Circumcision, M. Le Monier enquires into the quantity of the variation of the magnetic needle, observed by M. Bouvet at that place, and also into observations of the same kind, made at other places in the neighbourhood of it, about the same time, as well as both before and since. And by comparing these observations together, he concludes, that at the time when Captain Cook was in these seas, the variation of the needle at Cape Circumcision must have been 10° westerly: whereas, in the most westerly point of Captain Cook’s track, where he was sufficiently near the parallel of 54° south, to have seen land situated in it, the variation was 131⁄2° westerly. This difference of 31⁄2°, in the variation, answers to about 7° of longitude, in this part of the parallel of 54° south: and by so much did Captain Cook fall in with this parallel to the eastward of what he ought to have done to see the land in question. “Hence (M. Le Monier infers), that it is not surprising the British navigator should not find Cape Circumcision under a meridian which is 281⁄2° to the eastward of Ferro, when it is really situated under a meridian which is but 211⁄2° to the eastward of it.”
In replying to these allegations, I shall first show, that, granting the dependence which M. Le Monier supposes may be placed on observations of the variation made at sea, he has stated the quantity of the variation observed on board the Resolution, very erroneously.
Secondly, I shall prove, beyond contradiction, that observations of the variation, made at sea, cannot be depended on for the purposes to which M. Le Monier has applied them.
And, lastly, that no material error had crept into M. Bouvet’s reckoning; but that if any error did exist, it must have been of a contrary nature to that which M. Le Monier supposes.
That M. Le Monier has not given altogether a true representation of the matter, will appear from hence. On the 16th of February, at noon[27], the Resolution was in latitude 54° 311⁄2ʹ south, which is sufficiently near the parallel of 54° south, to see high land, the northern extremity of which lies to the southward of that parallel; and at that time we were in 6° east of Greenwich, or 233⁄4° east of the island of Ferro: that is, 43⁄4° less than is assigned for our situation by M. Le Monier. On the evening of the same day, the ship being in latitude 54° 24ʹ, and longitude 6° 30ʹ, or 241⁄4° east of Ferro, the variation was no more than 12° 7ʹ west, which also is near a degree and a half less then M. Le Monier says it was, when we first arrived in a proper parallel for seeing Cape Circumcision. It is true, the next morning, in latitude 54° 211⁄2ʹ south, longitude 8° 6ʹ east, we had 13° 42ʹ west variation; but this was after we had run more than two degrees within sight of the parallel of 54° south. It is, moreover, highly probable, that both these variations were too great; for, on the 17th, in the evening, latitude 54° 25ʹ south, and longitude 9° 20ʹ east; that is, 11⁄4° more to the eastward, and after we had run 31⁄3° on the parallel we were then on, the variation was no more than 13° 16ʹ west. It is also worthy of remark, that on the 14th, in the evening, latitude 56° 141⁄2ʹ south, and longitude 4° 50ʹ east, which is but 1° 10ʹ to the westward of the point, where the Resolution came first into a proper situation to see land, situated in the parallel of 54° south, the variation observed was no more than 6° 50ʹ west. And we may further add, that on the 1st of March, 1774, the Adventure had no more than 123⁄4° west variation, though she was then considerably both to the northward and eastward of our situation on the 17th of February in the morning, on both which accounts the variation ought to have been greater, instead of a whole degree less. From all these circumstances, there can be little doubt but that the two variations, observed by us on the 16th and 17th of February, were too great; or that the variation, at the point where the Resolution first came sufficiently near the parallel of 54° south, to see land, the northern extremity of which is situated in that parallel, could not be more than 111⁄2° west, instead of 131⁄2°, as M. le Monier has represented it.
Under this head of enquiry, I may also observe, that, although the Resolution was too much to the southward of the parallel of 54° south, when she crossed the meridian which is 211⁄2° to the eastward of Ferro, that is, 33⁄4° east of Greenwich, the longitude which M. Le Monier assigns for Cape Circumcision, to see if it had been in that situation, yet her consort, the Adventure, was for several degrees on each side of that meridian; and especially when she had 101⁄2° of west variation, full as near to the parallel of 54° south as M. Bouvet was to the land when he saw it[28]; and on the day that she actually passed that meridian, had fine clear weather.[29] Hence, therefore, granting M. Le Monier his own arguments, which, however, I have proved to be erroneous, and that observations made at sea, for the variation of the compass, may be depended on for the purpose of finding the longitude, it is utterly impossible that both the Resolution and Adventure could have passed Cape Circumcision without seeing it. But I shall now show, that these observations are liable to a much greater error than the whole quantity, so vigorously insisted on by this gentleman.
I will not here run the risk of incurring M. Le Monier’s displeasure, by calling the accuracy of M. Bouvet’s observations in question; but will admit every thing that he himself can think due to the instruments and observations of that deserving navigator. It is enough for my argument, and it is but too evident from the observations themselves, that ours were by no means capable of determining the variation to so small a quantity as that which M. Le Monier rests his whole cause upon; and if so, his arguments, which depend wholly on a supposition, that not only they, but M. Bouvet’s also, were capable of determining it with the utmost exactness, must fall to the ground.
1st, It appears, from various instances, that the variations observed by the same compass would differ 3° to 5°, 6°, and sometimes even 10°, from no other cause whatever, but putting the ship’s head a contrary way.[30]
2d, That the same compass, in the same situation in every respect, within a few miles, but at two different times of the same day, would give variations differing from one another, 3°, 4°, 5°, 6°, and even 7°[31].
3d, That the same compass, on the same day, and in the hands of the same observer, will give variations differing from one another by 5°, on board the same ship, when under sail, and when at anchor in a road-stead.[32]
4th, Compasses made by the same artists at the same time and place, but on board different ships, differed 3°, 4°, and even 5° in the variation.[33]
5th, The same compasses, on board the same ship, and within a few miles of the same situation, but at different times of our being there, gave variations differing by 4° and 5°, or upwards.[34]
6th, Different compasses, at the same time, on board the same ship, and in every respect under the same circumstances, will give variations differing from one another, 3°, 4°, 5°, and 6°.[35]
These differences, several of which happened very near the place in question, are all of them at least equal to, most of them much greater, and some of them double that which M. Le Monier founds his argument on, even according to his own account of it, which I have already shown is by no means admissible, and, therefore, totally invalidate it. To allege that the instruments made use of in Captain Cook’s two voyages were bad, or that the observers were not expert in the use of them, will answer no purpose: they are the instruments and observers which M. Le Monier’s argument must rest on; and, therefore, let those of the French, or any other navigator, have been ever so much better than they were (which few will be hardy enough to assert, and fewer still found weak enough to believe), it will avail nothing to the point in dispute, which must evidently fall to the ground, if the observations made for finding the variation in Captain Cook’s voyage are not sufficient to support it. What then must become of it, if M. Bouvet’s observations, of this kind, were liable to an equal, or a greater error? which, without any reasonable cause for offence, we might suppose they were.
It is not necessary to account for these differences in the observed variations in this place, nor yet to point out the reasons why such anomalies have not been noticed in observations of this kind before. I shall, however, remark, that I have hinted at some of the causes in my introduction to the observations which were made in Captain Cook’s second voyage; and many others will readily offer themselves to persons who have had much practice in making these observations, and who have attentively considered the principles on which the instruments are constructed, and the manner in which they are fabricated. Nor is it at all surprising, that the errors to which the instruments and observations of this kind are liable, should not have been discovered before, since no navigators before us ever gave the same opportunity, by multiplying their observations, and making them under such a variety of circumstances as we did.
Having now fully shown, that the circumstances, brought forward by M. Le Monier, in support of his argument, are neither such as can be depended on, nor yet fairly represented, I shall next attempt to demonstrate, that it is utterly improbable M. Bouvet could be out, in his account of longitude, so much as is here supposed, in the short run which had been made from the island of St. Catherine, the place they took their departure from: on the contrary, that there is sufficient reason to believe the error, of whatever magnitude it might be, was of a different nature from that contended for, and that the two ships, instead of being to the westward of their account of longitude, were actually to the eastward of it. For according to their journals, extracted from the archives of the French East-India Company, by M. D’ Apres, printed under his inspection, and published by Mr. Dalrymple, F. R. S. amongst other voyages made for the purpose of examining the southern parts of the Atlantic Ocean, the longitude, according to the Eagle’s run from St. Catherine’s, was, 26° 27ʹ, and according to the Mary’s, 26° 20ʹ east of Teneriff; that is, 9° 57ʹ, and 9° 50ʹ east of Greenwich, or 27° 43ʹ, and 27° 36ʹ east of Ferro. But the Mary, which went to the Cape of Good Hope, made 7° 13ʹ east longitude from the land in question, to that place. Consequently the Cape of Good Hope being in longitude 18° 23ʹ east of Greenwich, Cape Circumcision will be in 11° 10ʹ east of Greenwich, or 1° 20ʹ more to the eastward than the run by the same ship from the island of St. Catherine’s makes it. Again the Eagle made the difference of longitude between Cape Circumcision and the island of Rodrigues 49° 44ʹ; and by the observations of M. Pingre, this island is in 62° 50ʹ of east longitude from Greenwich: Cape Circumcision is therefore in 13° 6ʹ east of Greenwich, or 2° 9ʹ more to the eastward than by the Eagle’s run from St. Catherine’s. Hence, therefore, as the longitude of this land resulting from a comparison of that shown by each of the ships, on their making land at places where the longitude is exceedingly well determined, is greater than that which results from their run from St. Catherine’s, the longitude of which is not known with certainty within several degrees, we may infer, with great safety, that whatever the quantity of M. Bouvet’s error might be, when he is supposed to have seen Cape Circumcision, it must have been in defect, and not in excess, as M. Le Monier supposes it.
Christ’s Hospital,
April 20. 1784. W. WALES.