550 The Sniithsonian Institution 



volcanic openings of the shell, arranged in strata conforming 

 to the laws of hydrostatics ; or, in other words, with strata 

 of equal density decreasing in ellipticity toward the earth's 

 center." The same Report contains Professor R. S. Wood- 

 ward's vice-presidential address before the Section of Mathe- 

 matics and Astronomy of the American Association for the 

 Advancement of Science at the Toronto meeting in 1889. 

 This is a historical summary, under the title of " Mathematical 

 Theories of the Earth," of the principal propositions which 

 have been from time to time advanced in reference to the 

 same subject, and is an extremely satisfactory performance. 

 Closely related to these papers are Clarence King's "Age 

 of the Earth," reprinted in the Smithsonian Report for 1893; 

 and Sir Robert Ball's article on "The Wanderino-s of the 

 North Pole," in the same volume. The former is a valuable 

 contribution to physical geology, the author being, for the 

 most part, in harmony with Kelvin, Von Helmholtz, New- 

 comb, and other mathematical physicists, who have insisted 

 on a much shorter period of past life for the earth, in any- 

 thing like its present condition, than is usually claimed by 

 geological writers. The article of Sir Robert Ball, reprinted 

 from the Fortnightly Review, is a popular exposition of the 

 recent investigations regarding variation of latitude, in which 

 Doctor S. C. Chandler has been the leader. 



At an early period in its history the Smithsonian Institu- 

 tion recognized the importance of the art and science of 

 aeronautics. In the Report for i860 is an interesting letter 

 from "distinguished citizens of Philadelphia," requesting the 

 Institution to interest itself in a projected passage across the 

 Atlantic "by aeronautic machinery," evidently meaning a 

 balloon as the principal, if not sole, feature. To this Profes- 

 sor Henry replied, giving information regarding some winds 

 which might be depended upon for steadiness, and expressing 



