10 THE ELECTRIC TELEGRAPH. 



charges passing over the parts of a broken conductor enclosed 



in a glass tube, or by letters formed by spaces cut out 



of parallel strips of tinfoil pasted on square plates of 



glass. Such letters are shown in Fig. 3. An electric dis- 



charge from the interior coating of a Ley den jar, being sent, 



for instance, through the double strips of tinfoil, from the 



end marked -f to the end marked connected with the 



outer coating of the jar, a spark would pass over each of the 



intervening spaces at the same time, and the letter would 



. appear beautifully illumin- 



, ^^^^^ | ated in the dark. This ex- 



i ^"^^ CL""" *""""" periment of Reusser forms 



a yery common 



p '-'-- ' illustration of tension elec- 

 tricity in lecture rooms. 



Reusser further suggested 



to call the attention of the observer, at the distant station, 

 by firing an electric pistol by means of the spark. 



16. In Spain, about the same time, Don Silva read a paper 

 before the Academy of Sciences of Madrid, on a system of 

 telegraphing with a single wire, by means of continuations 

 of sparks, said, by the Magazin de Voigt, to have been carried 

 out, two years later> with no small success, by the Infanto 

 Antonio ; and Betancourt stretched a single line in the air, 

 over a space of twenty-seven miles, between Madrid and 

 Aranjuez. He employed a battery of Leyden jars and received 

 signals by observing the divergence of suspended pith balls. 



17. Cavallo was the next who strove to attain the perfec- 

 tion of a telegraph by means of frictional electricity. In 

 1795 he published his " Traite d-'filectricite," in which he 

 gives descriptions of his systems of electric signalling and 

 communication. He proposed to transmit letters and nu- 

 merals by combinations of sparks and pauses. His electric 

 alarm was based upon the explosion of a mixture of hydrogen 

 and oxygen gases or of gunpowder by the electric discharge. 



18. It is necessary here to depart a little from historical 

 order, to mention the last and most ingenious invention of 

 a telegraph worked by frictional electricity ; this was the 



