534 T^^^ Suiithsonian Institution 



was manifested and that he received assistance in continuing 

 his investigations. 



In the same year, 1859, the Smithsonian Report contains a 

 reprint of the highest importance on the subject of " Radiant 

 Heat." It included three reports on the " State of Knowledge 

 of Radiant Heat," made at the meetings of the British Asso- 

 ciation for the Advancement of Science in 1832, 1840, and 

 1854, by Professor Baden Powell. New ideas on the nature 

 of heat, based on the work of Joule, Helmholtz, Thomson, 

 and others, were just then beginning to prevail abroad, and 

 they were well known among a few in this country. The 

 reports of Powell, while dealing much more with experi- 

 mental results than with theory, were very suggestive. Full 

 accounts of Melloni's experiments were given, and some of 

 the early notions of Sir William Thomson about the origin of 

 the sun's heat. Nine years later, in the annual Report for 

 1868, the now well-established mechanical theory of heat was 

 fully exploited in three very important papers. The first is 

 on the " Recent Progress in Relation to the Theory of Heat," 

 by A. Cazin, and it covers about fifteen pages of the Report. 

 In the second, which is on the " Principles of the Mechanical 

 Theory of Heat," by Doctor Miiller, of Freiburg, the new 

 doctrines are fully gone into, and its thirty-five pages consti- 

 tute not only a strictly scientific, but an exceedingly attrac- 

 tive, exposition of the dynamical theory. The third paper is 

 Tyndall's celebrated Rede Lecture on " Radiation," delivered 

 in 1865, in which, as every one knows, the mechanical theory 

 has full sway. 



A large part of the Report for 1862 is devoted to a series of 

 lectures on the " Undulating Theory of Light," by President 

 F. A. P. Barnard. They constitute a tolerably exhaustive 

 treatise on the subject, largely mathematical, and including 

 a discussion of double refraction, polarization, interference 



