442 WRITINGS OF JOSEPH HENRY. [1859 



studied by the meteorologists of this country than by those 

 of Great Britain and France. 



It should be distinctly understood that the remarks which 

 have been made in this communication relate to the more 

 violent changes of the weather which occur in autumn, win- 

 ter, and spring. The thunder showers which occur almost 

 daily during the warm weather in summer have somewhat 

 of a local character, and commence at the same time and 

 frequently at the same hour for several days in succession, 

 at the same and dififerent places; but wherever they com- 

 mence they move eastward over the country until they are 

 exhausted. 



Professor Henry also spoke of the facts collected in regard 

 to the nature of American storms, and their connection with 

 the two great aerial currents continually flowing over the 

 temperate zone. He considered that the great changes of 

 the weather are principally due to the gradual production 

 of an unstable equilibrium in the two currents by the accu- 

 mulation of heat and moisture in the lower. 



He spoke in high terms of the importance of the labors 

 of Mr. Espy in developing the theory of the upper motion 

 of air and the evolution of latent heat in the production of 

 storms. 



In reply to a question as to the possibility of crossing the 

 Atlantic in a balloon, the Professor stated that he had little 

 doubt, if the balloon could be made to retain the gas and to 

 ascend into the upper current, it would be wafted across the 

 ocean in the course of three or four days. If it descended 

 into the lower current it would be carried to the north of 

 east, and if it continued in the upper current it would reach 

 Europe south of the same point. The course could be 

 changed, within certain limits, by ascending and descend- 

 ing from one current to the other. The late balloon voyage 

 from St. Louis to Jefferson county, New York, was of inter- 

 est in confirming the theoretical direction of the great lower 

 current of this latitude. 



