THE CENTURY'S PROGRESS IN METEOROLOGY 



perhaps the greatest of theoretical chemists, took the 

 question in hand, and solved it by showing that water 

 exists in the air as an utterly independent gas. He 

 reached a partial insight into the matter in 1793, when 

 his first volume of meteorological essays was published; 

 but the full elucidation of the problem came to him in 

 1801. The merit of his studies was at once recognized, 

 but the tenability of his hypothesis was long and ardently 

 disputed. 



While the nature of evaporation was in dispute, as a 

 matter of course the question of precipitation must be 

 equally undetermined. The most famous theory of the 

 period was that formulated by Dr. Hutton in a paper 

 read before the Royal Society of Edinburgh, and pub- 

 lished in the volume of transactions which contained 

 also the same author's epoch-making paper on geology. 

 This "theory of rain" explained piecipitation as due to 

 the cooling of a current of saturated air by contact with 

 a colder current, the assumption being that the surplus- 

 age of moisture was precipitated in a chemical sense, 

 just as the excess of salt dissolved in hot water is pre- 

 cipitated when the water cools. The idea that the cool- 

 ing of the saturated air causes the precipitation of its 

 moisture is the germ of truth that renders this paper of 

 Hutton's important. All correct later theories build on 

 this foundation. 



The next ambitious attempt to explain the phenomena 

 of aqueous meteors was made by Luke Howard, in his 

 remarkable paper on clouds, published in the Philosoph- 

 ical Magazine in 1803 the paper in which the names 

 cirrus, cumulus, stratus, etc., afterwards so universally 

 adopted, were first proposed. In this paper Howard^ 

 acknowledges his indebtedness to Dalton for the theory 



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