34 PROFESSOR HENRY AND THE 



tions, so that the same letter would appear at 

 the same time to both operators. By this appara- 

 tus, whose principle of synchronous revolution is 

 the same as that now used in the printing tele- 

 graph, the sender would simply close the circuit 

 on his electrical machine when his revolving 

 wheel presented the desired letter, and the pith-ball 

 electroscope, moving at the receiving end at the 

 same instant, would indicate to the receiver that 

 the letter then presenting itself to him on his 

 wheel was the one intended. 



A number of other inventors used static elec- 

 tricity for the same purpose during the latter years 

 of the last century, and the earlier ones of this. 

 In England, Ronalds had a line of eight miles 

 on which the wire was suspended from poles, 

 and insulated by silken strings;* and in 1796, 

 Salva, in Spain, worked a line by static electricity 

 twenty-six miles long.f 



In the year 1800 Volta produced the voltaic pile, 

 and gave to the world that new manifestation of 

 electricity called galvanism. In that form this 

 subtle agent is far more manageable than in 

 the form of static electricity; and by the use of 

 galvanic batteries a current of low tension, but 

 of enormously greater power, can be maintained 

 with little difficulty; whereas static electricity 



* See Appendix, Note G. 

 t See Appendix, Note H. 



