480 Mr. J. Trowbridge on the Motion of 



shows that the greatest rate of decrease of after passing the 

 maximum is only \ of its initial rate of increase. 



When 4>=\$ or =-2</>', 0=^-0'; 



when^=i^ or =3^', 0=^0'; 



and if <f> be further increased beyond 3<//, the rate of diminu- 

 tion of will become less and less rapid. 



We also notice that the maximum value of 6 is inversely 

 proportional to ah 2 , thus agreeing pretty closely with the 

 results of Prof. Perry's first experiments. 



When $ is large compared with <jf/ my formula gives 

 approximately 



a_ 15* 

 16EAa 3 <£" 



Owing, however, to our assumption that a<f> is small compared 

 with unity, little value can be attached to this result. It can 

 only hold if the strip is very thin indeed, and arf) is a small 

 quantity intermediate in order of magnitude between h[a and 

 unity. 



Cambridge; September 1890. 



LIV. Motion of Atoms in Electric Discharges. 

 By John Trowbridge*. 



I^HE 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 oscillating discharge of elec- 

 tricity 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 oscillating discharge passes are conveyed 

 to and fro by the oscillating discharge, or whether they are 

 shaken, so to speak, by the discharge so that they emit to the 

 aether the ripples which appeal to our senses as light and 

 heat. No mention is made here of a convection 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 Professor J. J. Thomson, director of the 



Cavendish Laboratory, Cambridge, England, appeared in the 



* Communicated bv the Author. 



