1 68 TRANSACTIONS OF tHE ILLINOIS 



primiti\e forests of the West, which disappeared at his approach and 

 desolation followed in his rear. The present arid, desolate condition of 

 Persia, Afghanistan, Beloochistan, Mesopotaniia, Syria, etc., countries 

 famous in history for their fertility, population, power, wealth, science, 

 and relinenient, shows that great climatic changes have taken place. Now 

 these changes must either have been wrought by human agency, 

 or by astronomical causes. If by the latter, then it must have been 

 by a physical change in the constitution of the Sun; as he is the 

 great vivifier not only of the Earth but of the universe. He 

 not only sets in motion the mainsprings of plant and animal life, 

 but with irresistible power and majestic grandeur he hurls our 

 globe and planets with inconceivable velocity around him through 

 space. Whatever of motion there is on the earth, in the ocean, the air, 

 or in the solar system, emanates from the energy of the sun. We know 

 planetaiy motions are not only uniform but invariable, not having changed 

 or deviated even a fractional jDart of a second since the days of Hipparchus,- 

 the first observer, two thousand two hundred years ago. Hence the energy 

 producing them must be constant, uniform, and invariable also. The 

 annual mean of all physical phenomena, hygrometric, meteorologic, elec- 

 tric, magnetic, thermal, etc., are also physical constants. It were there- 

 fore futile to look for the cause of climatic changes within the liistorical 

 period, to astronomical changes. Our only alternative then is to refer 

 them to human agency. Especially are we justified in so doing when all 

 admit that the natural operation of known physical laws is such as 

 to work these changes imder proper conditions; and that the opera- 

 tions of man can and do produce those conditions. Let us see how 

 this is. 



About three tenths of the earth's surface is land, the remaining seven 

 tenths being water. As the average annual energy of the sun is a phys- 

 ical constant, so the annual average of water vaporized from the ocean, 

 and consequently the annual average of rain precipitated must be phys- 

 ical constants also. Neither the area nor the physical condition of the 

 water surface of the earth has changed within the memory of man. 

 Hence, neither has the reaction of the ocean upon the atmosphere changed 

 within that time. Then, consequently, as far as rainfalls on the ocean 

 are concerned, other things being equal, the amount of rain on the water 

 surface must not have changed either. But how is it with the land sur- 

 face of the earth? In Europe, Asia, and Africa, where thousands of 

 years ago were impenetrable forests, there are now treeless and desolate 

 plains. The condition of the land surface of the earth being different 

 now than formerly, its reaction upon the atmosphere must also be differ- 

 ent. In respect to rain and drought, this reaction is as follows. Rain only 

 falls from an atmosphere that is cooling after taking up and holding 

 vapor in suspension at a higher temperature. Volumes of air nearly filled 

 to saturation with vapor, are constantly drifting over surfaces of lower as 

 well as higher temperature. Those drifting over surfaces of lower tem- 

 perature become cooled, clouds form over, and rain falls on such cool 

 surfaces. Now, which are the cooler, surfaces clothed with vegetation, 



