HOW THE WEATHER IS FORETOLD.

By James H. Flint.

In former times, the chief herald of the weather was the almanac, which ambitiously prophesied a whole year of cold and heat, wet and dry, dividing up the kinds of weather quite impartially, if not always correctly.

But the almanac, good as it was now and then, and the weather-wise farmers, correct as sometimes they might have been, were not always able to impart exact information to the country; and they have been thrown quite into the shade of late, by one who is popularly known under the somewhat disrespectful title of "Old Prob," or "Old Probabilities." He has become the Herald of the Weather to the sailor, near the rocky, dangerous coasts; to the farmer, watching his crops, and waiting for good days to store them; to the traveler, anxious to pursue his journey under fair skies; and to the girls and boys who want to know, before they start to the woods for a picnic, what are the "probabilities" as to rain.

Every one who reads the daily paper is familiar with the "Weather Record," issued from the "War Department, office of the Chief Signal Officer," at Washington. These reports give, first, a general statement of what the weather has been, for the past twenty-four hours, all over the country, from Maine to California, and from the Lakes to the South Atlantic States; and then the "Probabilities," or "Indications," for the next twenty-four hours, over this same broad territory. The annual reports of the Chief Signal Officer show that in only comparatively few instances do these daily predictions fail of fulfillment.

The reason these prophecies are so true is a simple and yet a wonderful one. The weather itself tells the observer what it is going to do, some time in advance, and the telegraph sends the news all over the country, from the central signal office at Washington.

We shall see, presently, how the weather interprets itself to "Old Probabilities." Although it has proved such a fruitful subject of discourse in all ages, yet I am afraid many people who pass remarks upon it do not really think what the weather is made of. Let us examine its different elements.

The atmosphere has weight, just as water or any other fluid, although it seems to be perfectly bodiless. We must comprehend that the transparent, invisible air is pressing inward toward the center of the earth. This pressure varies according to the state of the weather, and the changes are indicated by an instrument called a barometer. Generally speaking, the falling of the mercury in the tube of the barometer indicates rain, and its rise heralds clear weather. Sometimes the rise is followed by cold winds, frost and ice. What these changes really indicate, however, can be determined only by comparing the barometric changes, at certain hours, in a number of places very far apart. This is done by the Signal Service. Observations are made at about one hundred and forty stations, in different portions of the country, at given hours, and the results are telegraphed at once to Washington, where our faithful "weather clerk" receives them, reasoning out from them the "probabilities" which he publishes three times in every twenty-four hours.

But the atmosphere varies not only in weight, but also in temperature. The thermometer tells us of such changes.

Besides this, the air contains a great amount of moisture, and it shows as much variation in this characteristic as in the others. For the purpose of making known the changes in the moisture of the atmosphere, an instrument has been invented called a "wet-bulb" thermometer.

We are thus enabled to ascertain the weight or pressure, the temperature, and the wetness of the air, and now it only remains for us to measure the force, and point out the direction, of the wind. This is done by the familiar weather-vane and the anemometer. The vane shows the direction, and the anemometer is an instrument which indicates the velocity of the wind.

It is by a right understanding of all these instruments that the signal service officer is enabled to tell what the weather says of itself; for they are the pens with which the weather writes out the facts from which the officer makes up his reports for the benefit of all concerned. Thus, however wildly and blindly the storm may seem to come, it sends messengers telling just where it arose, what course it will take, and how far it will extend. But it tells its secrets to those only who pay strict attention.

The system of danger signals, adopted by the United States Government, has proved of great benefit to shipping. All along the coasts are stations, at which plainly visible signals are displayed, to warn ship-captains of approaching storms. The reports of observers at the stations are required to give all instances in which vessels have remained in port on account of official warnings given. In these cases danger was avoided, and statistics show that disasters to shipping have been considerably fewer since the introduction of the cautionary signals.

The agricultural interests of the country also have been greatly benefited by the daily bulletins sent to every farming district in the land by the Weather Department. These bulletins are made from telegraphic reports received at appointed centers of distribution, where they are at once printed, placed in envelopes, and addressed to designated post-offices in the district to be supplied. Each postmaster receiving a bulletin has the order of the Postmaster-General to display it instantly in a frame furnished for the purpose.

The bulletins reach the different offices, and are displayed in the frames, on the average, at eleven o'clock in the morning, making about ten hours from the time the report first left the chief signal officer until it appeared placarded at every center of the farming populations, and became accessible to all classes even in the most distant parts of the country.

The information given on these bulletins has been found especially valuable to those farmers who take an interest in the study of meteorology, or the science of weather, and the facts announced are so plain, that any intelligent person may profit by them. For instance, each bulletin now announces, for its particular district, what winds in each month have been found most likely, and what least likely, to be followed by rain. Attention given to this one simple piece of information will result in increasing the gains and reducing the losses of harvesting.

Warnings of expected rises or falls in the great rivers are made with equal regularity, telegraphed, bulletined in frames, and also published by the newspapers, at the different river cities. These daily reports give the depths of water at different points in the rivers' courses, and thus make it easy for river shipping to be moored safely in anticipation of low water, when ignorance might lead to the grounding of the boats on sand-bars or mud-banks. The notices of the probable heights which freshets may reach, are followed by preparations upon the "levees" and river-banks, to guard against overflows.

The United States Signal Service is a branch of the army. No one is admitted to it who is under twenty-one years of age. Every candidate has to undergo before enlistment an examination, the chief subjects of which are spelling, legible hand-writing, proficiency in arithmetic, and the geography of the United States, physical and political.

Successful candidates are regularly enlisted in the army, as non-commissioned officers, and go through a course of very systematic instruction in military signaling and telegraphy. They are assigned afterward to different posts, where they are required to make observations and report the same by wire three times a day, to the commanding officer at Washington. These observations are made by means of the instruments I have described, and include the different appearances in the sky; and at all the stations they are made at the same hour, according to Washington time. The telegraph gives to the Herald of the Weather and his aids the advantage of hearing from all the hundred and forty-odd observers almost at the same time; and when all this information has been gathered up, studied out, and re-arranged, the same swift servant takes all over the country, again almost at one time, the ripe results of the care and watching of more than seven score persons separated by hundreds and even thousands of miles from the central office.

I should like to describe the instruments fully, but must content myself with telling you what remarkable things some of them do. The self-registering barometer, for instance, is made to actually photograph a storm; another is made to draw with a pencil, every hour, figures that show the height of the column of mercury and the condition of the atmosphere. Even the vane, or weather-cock, marks down the direction and force of the wind.

The report of the chief signal officer for the year 1876 gives some idea of the vast amount of labor performed by the service. The Herald of the Weather never rests. As he says, "The duties of this office permit little rest and less hesitation. Its action must be prompt. * * * Its orders must issue, its signals of warning be given, and its record thus made, sometimes when wisdom would delay, if possible, and subsequent information show it had delayed rightly. It is the simple duty of the office to act at each present moment as well as it can with the information at that time before it. The reports to come after can only give bases for future action, while exhibiting the right and wrong of the past." These points should be borne in mind by those who are disposed to find fault with some of the daily predictions about the weather. If these predictions do not always come true, it is for the reason given above. Each report must be made at a given hour. Sudden changes may occur immediately after a report has been issued. These changes cannot be waited for, and cannot always be foreseen. But the general accuracy of the daily reports cannot be questioned, as about eighty per cent of their predictions are known to have been verified, and the average of failure grows less.

The method of arranging, comparing, and studying out the meaning of all the different records of observations made at all the weather stations, cannot be explained in a short article. But I may add that the weather is, after all, not quite so capricious as its accusers have asserted. And it has been found that all storms have certain "habits, movements, and tracks." It is by applying these laws, and drawing conclusions from them, that the prophet of the weather is able to tell so nearly what kind of a day we shall have, and just about where and when the storm will come.

Nearly all great storms have a rotary, or cyclonical character. The little whirlwinds we often see on windy days, when the dust is caught up and whirled around, are miniature examples of great storms which sweep around immense circles. Almost all great rain, hail, and snow storms revolve in this manner around a calm center where the mercury is low in the tube of the barometer. Sometimes two or more cyclones meet, and interfere with one another's rotary motions; and "when interferences of this description take place, we have squalls, calms (often accompanied by heavy rains), thunder-storms, great variations in the direction and force of the wind," and irregular movements of the barometer.

So then, considering all that the Herald of the Weather has to do, the care and quickness with which it must be done, and the excellent results he obtains, everybody who is at all interested in the changes of the weather ought to be grateful to him for his faithfulness and devoted attention to duty.

But why should the Government of the United States—that is to say, the people as a whole—take the trouble and bear the cost of keeping a small army of men to watch the weather all over the country, and to telegraph their observations three times a day to Washington? Why should the officials there take the trouble to compare these observations and telegraph back to each locality what weather it may expect, and what the weather will be elsewhere, so that you and I may know when to stay at home, or when to take our umbrellas with us if we go out?

Hardly. There are more important matters at stake. Most of you are old enough to know that it is unexpected weather that causes most of the trouble that the weather occasions. The farmer expects fair weather, cuts his hay or grain, and a storm comes and spoils it. He looks for rain, and lets his crop stand; the bright sun injures it, or he loses a good chance to harvest it. The ship-master expects fair weather, puts out from port, and his ship is driven back upon the shore, a wreck. He expects a storm, stays in port, and misses the fair wind that would have carried him far to sea.

Now, a very large part of these disappointments and losses may be prevented, if one only knows with reasonable certainty what sort of weather it is likely to be to-day and to-morrow; and that is just the information the Weather Herald furnishes. The great storms usually come slowly driving across the country—so slowly that the telegraph may send word of their coming two or three days ahead. Thus the farmers may know just what they may safely undertake to do; and so may the ship-masters.

Since the farmers and seamen have learned to value the weather warnings rightly, this service saves the country every year millions and millions of dollars' worth of property, and, it may be, hundreds of lives. Often a single timely warning has prevented losses that would have amounted to more than the entire cost of the weather service from the beginning until now. And possibly the yearly saving effected by warnings of ordinary "changeable" weather, may together amount to more than those in connection with great storms.