The Three Secretaries 135 



in his testimony before the Supreme Court in 1849, he, with 

 characteristic modesty, alluded to Steinheil as a discoverer of 

 this use of the earth. 1 In 1876, however, with the fuller 

 knowledge which he then possessed, he wrote to Reverend 

 S. B. Dod in Princeton : 



" I think the first actual line of telegraph, using the earth 

 as a conductor, was made in the beginning of 1836. A wire 

 was extended across the front campus of the college grounds, 

 [in Princeton] from the upper story of the library building to 

 the philosophical hall on the opposite side, the ends termi- 

 nating in two wells. Through this wire, signals were sent, 

 from time to time, from my house to my laboratory." 2 



Another step was his device, used in Princeton as early as 

 1833, of opening one circuit by means of another. By this 

 he was able to carry out his plan of utilizing the power of a 

 quantity magnet at great distances, through the agency of the 

 more sensitive intensity magnet. Of the utmost importance 

 has this combination proved to the telegraph its principle 

 underlying all the various forms and uses of the relay magnet 

 and the receiving magnet and local battery since employed. 3 



"One morning," writes Professor Trowbridge, "he came 

 into my laboratory at Cambridge, and, after I had shown him 

 various pieces of scientific apparatus, he stood before an elec- 

 tro-magnet which was working a relay and looked long at 

 the magnet, and then at the battery which was coupled for 

 quantity, and remarked in a quiet tone, as if half to himself, 

 1 If I had patented that arrangement of magnet and battery 

 I should have reaped great pecuniary reward for my discovery 

 of the practical method of telegraphy.' " 



1" Smithsonian Report," 1857, page 113. 3 A circuit-breaker made and used by 



2 " Memorial of Joseph Henry," 1880, Henry in Princeton is now in the United 

 page 150. States National Museum. 



