THE PROGRESS OF PHYSICS IN THE NINETEENTH 



CENTURY 



BY CARL BARUS 



[Carl Barus, Dean of the Graduate Department, Brown University, b. February 19, 

 1856, Cincinnati, Ohio. Ph.D. Columbia University, University of Wiirzburg, Ba- 

 varia. Physicist, U. S. Geological Survey; Professor of Meteorology, U. S. 

 Weather Bureau; Professor of Physics, Smithsonian Institution; Member of the 

 National Academy of Science of the United States; Vice-President of American 

 Association for the Advancement of Science; Corresponding Member of the 

 British Association for the Advancement of Science; Honorary Member of the 

 Royal Institution of Great Britain; President of American Physical Society; 

 Rumford Medalist. Author of The Laws of Gases; The Physical Properties of the 

 Iron Carburets ; and many other books; contributor to the standard magazines.] 



You have honored me by requesting at my hands an account of 

 the advances made in physics during the nineteenth century. I have 

 endeavored, in so far as I have been able, to meet the grave respon- 

 sibilities implied in your invitation; yet had I but thought of the 

 overwhelmingly vast territory to be surveyed, I well might have 

 hesitated to embark on so hazardous an undertaking. To mention 

 merely the names of men whose efforts are linked with splendid 

 accomplishments in the history of modern physics would far exceed 

 the time allotted to this address. To bear solely on certain subjects, 

 those, for instance, with which I am more familiar, would be to de- 

 velop an unsymmetrical picture. As this is to be avoided, it will be 

 necessary to present a straightforward compilation of all work above 

 a certain somewhat vague and arbitrary lower limit of importance. 

 Physics is, as a rule, making vigorous though partial progress along 

 independent parallel lines of investigation, a discrimination between 

 which is not possible until some cataclysm in the history of thought 

 ushers in a new era. It will be essential to abstain from entering 

 into either explanation or criticism, and to assume that all present 

 are familiar with the details of the subjects to be treated. I can 

 neither popularize nor can I endeavor to entertain, except in so 

 far as a rapid review of the glorious conquests of the century may be 

 stimulating. 



In spite of all this simplicity of aim, there is bound to be distortion. 

 In any brief account, the men working at the beginning of the cen- 

 tury, when investigations were few and the principles evolved neces- 

 sarily fundamental, will be given greater consideration than equally 

 able and abler investigations near the close, when workers (let us be 

 thankful) were many, and the subjects lengthening into detail. 

 Again, the higher order of genius will usually be additionally exalted 

 at the expense of the less gifted thinker. I can but regret that these 

 are the inevitable limitations of the cursory treatment prescribed. 



