ADDRESS OF THE PRESIDENT. 57 



Another experimenter of great renown was Regnault. His most noted 

 work was in improving the thermometer and determining the laws of the 

 expansion of gases, vapor pressure, specific heat of water, and the elastic 

 force of steam. These studies led to one of the most important accomplish- 

 ments of the century, the liquefaction of all gases. This was first done in 

 1877 by Pietet and Cailetet when they reduced oxygen, nitrogen, hydrogen 

 and air to the liquid state. 



Carnot created the science of thermo-dynamics or the dynamics of heat. 

 Lord Kelvin and others were contributors to this science. 



The mechanical theory of heat naturally led to tiie docti'ine of the con- 

 servation of energy. This doctrine was first stated by Robert Mayer, a 

 German physician in 1842, but the heat equivalent of mechanical energy 

 was first determined by Joule in 1847 and further proved by Lord Kehdn, 

 Helmholtz and Tyndall. 



The establishment of the undulatory or wave theorj' of light is one of the 

 great achievements of the century. This was due to Thomas Young, an 

 Englishman, and Fresnel, a Frenchman. As a result of this conception, other 

 discoveries followed, such as spectrum analysis, polarization of light and the 

 determination of the velocity of light. 



The most marvelous achievements of the century in physics have been 

 in electricity and magnetism. We are tracing the scientific thouglit and not 

 primarily the application to the needs of man. 



Just before the opening of the century the discovery of the Galvanic 

 battery by Galvani and Volta made possible the future developments. The 

 next discovery was by the Danish physicist Oersted which showed the close 

 relationship of electricty and magnetism. The electro-magnet was the result. 

 This paved the way for the electric telegraph which Joseph Henry first made 

 in 1832 but was made practical by Morse in 1844. 



The conversion of electricity into mechanical energy was made possible 

 by Oersted, Arago, Ampere, Sturgeon and Henry. This gave rise to motors. 

 Another discovery was necessary; how to convert mechanical energy into 

 electricity. This was accomplished by Michael Faraday. This gave us the 

 dynamo, but it was nearly half a century before it came into practical use. 

 In 1831, Faraday also discovered the principle of induction. This greatly 

 improved the telegi'aph and made possible the telephone. To Graham Bell 

 is due the honor of having made the first telephone for practical use. 



The past twenty-five years has been marked by continuous and per- 

 sistent research and many new discoveries are being made. Maxwell's theory 

 of electric waves and its verification in 1888 by the German physicist Hertz, 

 laid the foundation for the wireless telegraph of Marconi in 1907- 



The wonderful experiments of Sir William Crookes in passing an electric 

 current through a high vacuum and experiments in radiant matter were 

 preliminary to the discovery of the X-rays by Roentgen of Germany in 1895. 

 The radio-activity of matter noAv is attracting much attention. Research 



