134 The Smithsonian Instihition 



this time a statement that the improvements made by him 

 were "directly appHcable to the project of forming an electro- 

 magnetic telegraph."^ 



In other words, he was the first to construct and use an 

 electro-magnetic acoustic telegraph of a type similar to that 

 which is at present more generally employed than any other 

 form. The code of signals now in general use was yet to be 

 invented. Provided with such a code, any operator could, by 

 the use of Henry's apparatus, have transmitted, in 183 1, mes- 

 sages of unlimited length, though of course at slow speed. ^ 



Before Henry made his magnets, and his discoveries in re- 

 lation to them, the telegraph was an impossibility, for until 

 then science was not ripe for the telegraph. Henry's inten- 

 sity magnet was the only electro-magnet which had ever 

 responded to electrical influence at any distance. Before it 

 was created there could be no electro-magnetic telegraph. 

 Equally essential was his discovery of the law by which mag- 

 net and battery were bound together in mutual proportion. 



Henry was also the first to use the earth for a return cir- 

 cuit, although the credit for this is usually given to Steinheil. 

 This practice was in some degree foreshadowed by Watson 

 and Franklin, both of whom used water to conduct a return 

 current. Watson in this manner lighted alcohol on the further 

 side of a pond ; Franklin, across the river Schuylkill. Watson 

 passed a current through the earth ; Franklin immediately 

 showed by experiment that this was due to the constant 

 moisture of the earth. It was Henry, however, who first 

 practically used the earth for a return current. It is true that 



3 Atnerican Journal of Science, January, telegraph was the invention of the steel style 



1831, Volume XIX, page 404. in the extremity of the sounding lever, and a 



2 The introduction of the second voltaic bat- grooved roller into which it could strike the 



tery rendered possible results in respect to paper as it was drawn onward over the roller 



speed not at that time within the range of to emboss upon it the alphabetical characters, 



human achievements. All that was needed (F. O. J. Smith, letter to the Regents of the 



to perfect Henry's invention into a recording Smithsonian Institution, March 30, 1S72.) 



