Page:Popular Science Monthly Volume 16.djvu/48

38 destructive. But all these instances are peculiarities singled out from a variety of items, highly interesting to any one contemplating either a temporary or permanent residence in a place new to him. The storms, the rain, and the snow he has to encounter; the average humidity and tenuity of the air he has to breathe; the variety and character of the winds that are to blow upon him; the mean and extreme of the daily, monthly, and yearly temperature to which he will be subjected; the relative number of cloudy and clear days—all this, constituting the climate of a place, should be known to one ere he hazards his comfort, his good feeling, or, it may be, his health, by a change of residence. And it is probable that, with the great number of observers now carefully noting and recording these items in various cities, the day is not far distant when their laborious experience of long years will be classified, reduced, and published in such a compendious form, that a stranger to any given place may, by half an hour's study of this publication, inform himself correctly as to its climate.

The solution of the third phase of the problem is the one productive of most immediate benefit to all, how much soever their callings may differ; and this universal interest warrants my stating its conditions more at length than I have done with the other two. This phase may be likened unto an algebraic equation—a combination of known and unknown quantities, which, being operated upon according to certain rules, gives a desired result.

First, to determine the known quantities, a variety of instruments must be read and recorded at stated periods. These are, anemometers, to indicate the direction and velocity of the wind; barometers, to measure the pressure of the air; and hygrometers, its humidity. Suppose sets of these, standard in quality, to be furnished a corps of trained observers stationed at various points throughout a given area, say a thousand square miles; let each observer note his instruments at predetermined hours, or, better, let the observation be automatic and continuous, which is now often done by means of mechanical contrivances; let a network of telegraphy connect all the stations with some central point: then, at any moment he wishes, a person at this point can ascertain the prevailing weather all over the area, or, in other words, the known quantities of his equation. Now, the atmosphere that encircles our globe is but an ocean of less density than the watery element that surges upon its surface; like that, it moves, contracts, and expands according to well-known physical laws, and these laws constitute the rules whereby the person at the central station operates on his known quantities, solves the equation, and obtains for a result the forecast of the weather for the next few hours.

Having a due regard for the conformation of the ground over which his prognostics extend, he well knows that, according to the relative variation of pressure, temperature, and moisture, there will be a corresponding variability of weather: that if the pressure is great