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.