MODERN CONCEPTS IN PHYSICS AND THEIR RELATION 



TO CHEMISTRY^ 



Bv Irving Langmuir 



Only about J^5 years ago, during the nineties of the hist century, 

 knowledge of the physical sciences had advanced to such a point 

 that many of the foremost physicists and cliemists began to be- 

 lieve that the rate of progress of fundamental knowledge must be 

 slowing up. The concepts of length, mass, time, energy, temperature, 

 electric, and gravitational fields, etc., had been given precise meanings 

 and were regarded as having an absolute existence quite as certain 

 as that of matter itself. The phenomena of nature were explainable 

 in terms of natural laws expressing relations between these absolute 

 (}uantities. It seemed that the most important of these laws of 

 |)hysics and chemistry had already been discovered and that the work 

 that remained to do was largely a matter of filling in the details 

 and applying these great principles for practical purposes. 



The laws of mechanics had been verified ex])erimentally with a 

 high degree of precision so no one doubted that they were rigorous 

 laws of nature. Back in about 1830, Hamilton had succeeded in 

 generalizing these laws in a few simple equations which seemed 

 to contain all the essential truths of mechanics. It was only necessary 

 to know how the kinetic and potential energy of any given system 

 varied with the momentum and the coordinates of its parts in order 

 to have at least a formal solution of the way in which the system 

 would behave at all times. Thus all future work in mechanics need 

 only be considered an application of Hamilton's equations. 



Complete knowledge of the nature of light presented more diffi- 

 culties. Hamilton, about 1820, showed that all the known laws of 

 geometrical optics could be explained quantitatively in terms of either 

 a corpuscular theory of light or a wave theory. The experiments of 

 Fresnel on the interference of light which were made about this 

 time, seemed to disprove Newton's corpuscular theory, so that Hamil- 

 ton's proof of the complete analogy between waves and corpuscles 



' Tresldontlnl address before the sevenfy-elKhth meeting of tlie Amerlcnn Chemical 

 .Society, Minnenpolls, MInii., Sept. 11, 1920. Reprinted by permission from the General 

 Electric Uevlew, vol. 32, No. 12. December, 11)20, 



219 



