Page:Popular Science Monthly Volume 78.djvu/34

30 volume classifying as "paradoxers" all those who believed in squaring the circle, or in perpetual motion, or that the world is flat, or that the sun do move. They can believe the impossible. It is the same way with those who expect great mechanical work to be done without the expenditure of a corresponding amount of force or energy. The law of the conservation of energy runs all through meteorology as it does through the mechanics of nature everywhere. Energy and work may be transformed to and fro, but never destroyed nor created by man.

I have no doubt that we shall some day long years hence acquire some control of the atmosphere, but at the present time we are not ready for it, neither scientifically nor socially. I say socially because if A could make it rain when his neighbor B wants dry pleasant weather, we should have grumbles and lawsuits and socialistic eruptions far worse than now.

I dare say that if ever we are to follow in the footsteps of Franklin who deprived lightning of its terror, or of Eedfield who taught the mariner how to avoid the dangers of the storm-center, we must adhere closely to nature: when once we know the details of her methods, then we may hope to learn how to make or to prevent the weather. To this particular study of the formation of rain, John Aitken, of Scotland, Carl Barus, of Brown University, and C. T. E. Wilson, of Cambridge, England, have especially contributed by their laboratory experiments. It is a question on which meteorological observers and laboratory physicists must labor together.

In India the prediction of great droughts has long been held to be one of the most important questions that can be attacked by the weather bureau of that country, and eminent men have worked upon it for twenty years past. The progress of their studies has gradually led us to see that the moist air of the southwest monsoon from which the rain falls has come from an unexpectedly great distance, namely, from the southern Indian Ocean. As you see on this globe before you, during the Asiatic winter season we have northeast trade winds here, and southeast trade winds there, south of the equator; but in the Asiatic summer season the heated air of the great continent of Europe, Asia and Africa, produces such an immense disturbance that over a large portion of the Indian Ocean the southeast trade wind disappears, or rather is turned about and flows northward over the equator to the region of the northeast trade, which is also turned about, and both combine to feed the great southwest monsoon of Asia. Knowing the origin of this moist monsoon, we shall be able to determine the probability of droughts or rains in India when we know whether the supply of air is sufficient and whether it will flow over the right region, or whether it will be deflected away from India. But to settle this question is at present very difficult.

The flow of any current of air is determined largely by the pressure