30 THE POPULAR SCIENCE MONTHLY 



esting 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 phys- 

 icists 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 north- 

 east trade, which is also turned about, and both combine to feed the 

 great southwest monsoon of Asia. Knowing tlie 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 suflBcient 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 diJQBcult. 



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



