ADDRESS OF PROF. S. NEWCOMB. 447 



to the east. The conckisions of these experiments are now too 

 familiar to need discussion. We can only regret that the American 

 physicist did not immediately publish his first experiments. 



In this same paper Professor Henry appears as the first ob- 

 server of another previously unnoticed phenomenon, sometimes called 

 the self-induction of the current. A vivid spark is seen when a 

 current through a long wire of considerable resistance is suddenly 

 broken by withdrawing the wire from the cup of mercury through 

 which the connection is produced. The longer the conducting 

 wire and the larger the plates of the battery, the more vivid the 

 spark. He attributes it to the long wire becoming charged with 

 electricity, which by its reaction on itself projects a spark when the 

 connection is broken.* The same discovery was independently 

 made two or three years later by Faraday^ who does not appear to 

 have noticed Henry's description of the phenomenon. 



Shortly after this Professor Henry was called to the chair of 

 natural philosophy in Princeton College. Although the duties of 

 an American college professor seldom allow much time for original 

 investigation, he soon resumed his electrical researches, and the first 

 of a regular series was communicated to the American Philosophical 

 Society in 1835. On February 6 of that yeat he continued the 

 subject of the self-induction of the electric current with especial 

 reference to the influence of a spiral conductor upon it. The series 

 of experiments on this subject are very elaborate, but cannot be 

 fully described without going into a series of minute details. 



On November 2, 1838, he presented an extended paper on Elec- 

 tro-Dynamic Induction, f He states that since tlie discovery of 

 magneto-electricity by Faraday in 1831 attention had been almost 

 exclusively devoted to the induction of electricity from magnetism. 

 He had therefore been engaged in reviewing and extending the 

 purely electrical part of " Faraday's admirable discovery " in the 

 direction indicated in the title. 



Among the least known works of Professor Henry during this 

 period are his researches upon solar radiation and the heat of the 



* American Journal of Science, Series I, Volume xxii, 1832, page 408. 

 ' t Transactions of the American Philosophical <8bcie<y,' Volume vi, page 308. 



