192 PROCEEDINGS OF THE AMERICAN ACADEMY 



Investigations on Light and Heat, made and pcblisued wholly oe in paet with 

 Appboprlation fkom the Kcmford Fund. 



XI. 



MOTION OF ATOMS IN ELECTRICAL DISCHARGES. 



By John Trowbridge. 



Presented October 8, 1890. 



The application of Spectrum Analysis to the measurement of the 

 approach or recession of a star in a direction directly away or directly 

 toward an observer's eye is generally regarded as one of the greatest 

 achievements of modern science. Experiments upon the oscillatory 

 discharge of electricity led me to reflect whether the method which 

 has been used in star observation might not be employed to test the 

 question whether the atoms of the metals of the terminals between 

 which the oscillatory discharge passes are conveyed to and fro by the 

 oscillatory discharge, or whether they are shaken, so to speak, by the 

 discharge, so that they emit to the ether the ripples which appeal to 

 our senses as light and heat. No mention is made here of a convec- 

 tion effect which would take place too slowly to give a spectroscopic 

 effect. 



After I had made the experiments which I will shortly describe, 

 and while I was in doubt whether to publish my results, a paper by 

 Prof. J. J. Thomson, Director of the Cavendish Laboratory, Cam- 

 bridge, England, appeared in the August number of the Philosophical 

 Magazine (1890), "On the Velocity of the Transmission of Electric 

 Disturbances," which contains the following passage : " The very 

 rapid rate with which the electric discharge is propagated through 

 a rare gas compels us to admit that the electricity is not carried by 

 charged atoms moving with this velocity. For if it were, then if the 

 discharge were to take place in air at atmospheric pressure between 

 two parallel plates one centimeter apart, charged to a potential dif- 

 ference of approximately 30,000 volts, the kinetic energy which would 

 have to be communicated to the atoms to make them move with this 

 velocity would be greater than the original potential energy of the 



