398 POPULAR LECTURES AND ADDRESSES. 



or down to about 200 C. below the temperature 

 of freezing water, or to within 73 of absolute cold. 

 Such changes as these actually take place in 

 masses of air rising in the atmosphere to heights 

 of eight or nine kilometers, or of twenty or twenty- 

 five kilometers. Corresponding differences of 

 temperature there certainly are throughout the 

 fluid mass of the sun, but of very different 

 magnitudes because of the twenty- sevenfold 

 greater gravity at the sun's surface, the vastness 

 of the space through which there is free circulation 

 of fluid, and last, though not least, the enormously 

 higher temperature of the solar fluid than of the 

 terrestrial atmosphere at points of equal density in 

 the two. This view of the solar constitution has 

 been treated mathematically with great power by 

 Mr. J. Homer Lane, of Washington, U.S. A., in a very 

 important paper read before the National Academy 

 of Sciences of the United States in April, 1869, 

 and published with further developments in the 

 American Journal of Science, for July, 1870. Mr. 

 Lane, by strict mathematical treatment finds the 

 law of distribution of density and temperature all 



