ON SOME MARVELS IN TELEGRAPHY. 26-? 



vibratingly towards and from the electro-magnet, without 

 producing actual contact Now, the current which was 

 passing along the coil round the electro-magnet changed in 

 strength with each change of position of this small piece of 

 metal The more rapid the vibrations, and the greater 

 their amplitude, the more rapid and the more intense were 

 the changes in the power of the electric current Thus, the 

 electro-magnet at the other station underwent changes of 

 power which were synchronous with, and proportionate to, 

 those changes of power in the current which were produced 

 by the changes of position of the vibrating piece of clock- 

 spring. Accordingly, the piece of clockspring at the receiv- 

 ing station, and with it the drumhead there, was caused by 

 the electro-magnet to vibrate with the same rapidity and 

 energy as the piece at the transmitting station. Therefore, 

 as the drumhead at one station varied its vibrations in re- 

 sponse to the sounds uttered in its neighbourhood, so the 

 drumhead at the other station, varying its vibrations, emitted 

 similar sounds. Later, the receiving drumhead was made 

 unlike the transmitting one. Instead of a membrane carry- 

 ing a small piece of metal, a thin and very flexible disc of 

 sheet-iron, held in position by a screw, was used. This disc, 

 set in vibration by the varying action of an electro-magnet, 

 as in the older arrangement, uttered articulate sounds cor- 

 responding to those which, setting in motion the membrane 

 at the transmitting station, caused the changes in the power 

 of the electric current and in the action of the electro- 

 magnet 



At the meeting of the British Association in 1876 

 Sir W. Thomson gave the following account of the perform- 

 ance of this instrument at the Philadelphia Exhibition : 

 " In the Canadian department" (for Professor Bell was not at 

 the time an American citizen) " I heard ' To be or not to be 

 there's the rub,' through the electric wire ; but, scorning 

 monosyllables, the electric articulation rose to higher flights, 

 and gave me passages taken at random from the New York 

 newspapers : 'S. S. Cox has arrived ' (I failed to make out 



