MAGNETIC TELEGRAPH. 17 



In still further pursuing his researches into the 

 subtle phenomena of electricity, Henry made, here 

 in Princeton, another capital discovery, this time 

 in advance of Faraday, which forms an important 

 element in the science of electricity. It is to 

 be found detailed in any school book, under the 

 name of " Henry's Coils." His wonderfully elab- 

 orate investigations will be remembered by the 

 students of that day; as it was conducted in part 

 in the open air. Wires stretched across the cam- 

 pus, in front and in rear of Nassau Hall, were 

 the means by which the questioner was cross- 

 examining nature, and wresting from her reluct- 

 ant grasp her hidden secrets. At that time tele- 

 graph wires did not exist; and those fine lines 

 traced across the sky, excited the liveliest interest 

 in the students, whose fantastic guesses as to their 

 significance were the cause of much pleasantry in 

 the idle hours. 



In the course of these investigations it was also 

 the good fortune of our scientist to first discover 

 the very curious phenomenon of "self induction," 

 as it is now called, which plays so important a 

 part in the creation and use of electric currents on 

 wires, sometimes injuriously and sometimes ben- 

 eficially. Without the knowledge of its laws no 

 duplex or quadruplex telegraph could be practically 

 operated; with that knowledge it can be neutral- 

 ized when it is injurious, and made available when 



