SKETCH OF JAMES P. ESPY. 837 



a distinguished professor, that I had failed to convince men. of 

 science of the truth of my theory, and that I had appealed to 

 the people, who are incapable of judging. It became, therefore, 

 necessary to obtain authority against authority." 



The origin of the studies iipon which the theory of storms is 

 based is traced in the opening paragraph of the " Philosophy " to 

 the result described by Dalton, that the quantity of vapor in 

 weight, existing at any time in a given place, could be deter- 

 mined by means of a thermometer and a tumbler of water cold 

 enough to condense on its outside a portion of the vapor in the 

 air. " It occurred to me at once," Prof. Espy says, " that this was 

 the lever with which the meteorologist was to move the world. I 

 immediately commenced the study and examination of atmos- 

 pheric phenomena, determined to discover, if possible, what con- 

 nection there is between rain and the quantity of vapor in the 

 atmosphere." Prof. Espy prefaced his paper in the British Asso- 

 ciation by saying that he had found, by examining simultaneous 

 observations in the middle of storms and all round their borders, 

 that the wind blows inward on all sides of a storm toward its cen- 

 tral parts ; toward a point if the storm is round, and toward a 

 line if the storm is oblong, extending through its longest diame- 

 ter. The theory is, in brief, that every atmospheric disturbance 

 begins with the ascension of air that has been rarefied by heat. 

 The rising mass dilates, and, as its temperature falls, precipitates 

 vapor in the form of clouds. Owing to the liberation of the 

 latent heat, the dilatation continues with the rising till the moist- 

 ure of the air forming the upward current is practically ex- 

 hausted. The heavier air flows in beneath, and, finding a dimin- 

 ished pressure above it, rushes upward with constantly increasing 

 violence. The great quantity of aqueous vapor precipitated dur- 

 ing this atmospheric disturbance gives rise to heavy rains. Much 

 of this theory still holds good ; but it has been found that the 

 motion of the wind in storms is rotary. 



Besides his explanation and proofs of this theory. Prof. Espy 

 presented to the British Association a paper on " Four Fluctua- 

 tions of the Barometer." The theory was more fully elabo- 

 rated in "The Philosophy of Storms," which was published in 

 a large octavo volume by Little, Brown & Co., Boston, in 

 1841, and was re-enforced by detailed descriptions of a large 

 number of storms occurring on the land and the ocean, the 

 course of which the author had been able to follow and study 

 with considerable accuracy. It also contained his answers to the 

 citicisms which had been made against his theory in the British 

 Association and elsewhere by prominent men of science and rival 

 meteorologists. In it, furthermore, he defended his theory that 

 storms could be produced by large fires making local disturb- 



