220 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 19 30 



in the case of geometrical optics became only of academic interest. 

 Through the study of the phenomena of interference, diffraction, 

 polarization and absorption of light, the wave theory of light became 

 firmly established. Light was supposed to consist of waves in some 

 sort of an elastic medium which was called the ether. 



About 1830, Faraday developed clear conceptions regarding the 

 electric and magnetic fields and Maxwell, about 1860, by applying 

 exact mathematical methods evolved the electro-magnetic theory of 

 light according to which light waves consisted of fluctuating electric 

 and magnetic fields which are propagated through space at a speed 

 which could be calculated from electric and from magnetic measure- 

 ments in a laboratory. 



Although the acceptance of Maxwell's views came slowly one 

 could not long remain skeptical after the production of electro- 

 magnetic waves of relatively great wave length by Hertz in 1884. 

 It may also be said that Maxwell's theory was essentially an applica- 

 tion of the mathematical methods which Hamilton had originated in 

 his treatment of the laws of mechanics, to Faraday's concepts of 

 electricity and magnetism. 



Thus in 1895, the physicists seemed to have some justification for 

 the attitude that the most important laws had been discovered. The 

 laws of mechanics had not been improved upon in 65 years. Fara- 

 day and Maxwell had brought in precise conceptions of electric and 

 magnetic phenomena and had shown that by classical methods like 

 those which had been so successful in mechanics, all the laws of optics 

 could be derived from those of electromagnetism. 



In chemistry a somewhat similar state had been reached. After 

 the evolution of the conception of the elements and of com- 

 bining proportions based upon an atomic theory, rapid progress 

 was made in accumulating data regarding the elements and their 

 compounds. Faraday's laws of electrolysis and new methods for 

 the accurate determination of atomic weights began to provide the 

 chemist with quantitative laws almost as precise as those of the 

 physicists. The work of J. Willard Gibbs had brought into chemistry 

 rigorous laws as fundamental in their field of application as were 

 those of Hamilton and Maxwell in physics. 



These remarkable advances on the quantitative side seemed to 

 overshadow in importance the more qualitative results that had 

 previously been obtained through the stimulus of the atomic theory. 

 Under the leadership of Ostwald, chemists began to adopt a much 

 more critical attitude and began to distinguish carefully between 

 what they considered experimental facts and hypotheses based upon 

 these facts. Ostwald, although he recognized the convenience of 

 the atomic theory, believed it must always remain impossible to 



