\/A' WILLIAM 



a combination of them, could be conveyed to a distance by 

 means of an electric circuit, including at both stations a powerful 

 electro-magnet. In striking any one of the tuning-forks differ- 

 ential currents were set up which caused the vibration of the corre- 

 sponding tuning-fork at the distant station, and thus communicated 

 the original sound. In 18G2 Reiss enlarged upon this ingenious 

 suggestion in attempting to convey the varying vibrations of a 

 diaphragm agitated by atmospheric sound-waves. His apparatus 

 consisted of a parchment diaphragm with a thin platinum wire 

 attachment set into vibration by sound, which caused a series of 

 contacts to be made, and the galvanic currents thus sent through 

 an electric circuit produced sounds by the making and unmaking 

 of an electro-magnet at the distant station. 



This instrument transmitted currents only of equal intensity, and 

 produced therefore sounds of equal calibre, distinguishable only 

 by their periods. It was thus capable of transmitting simple tunes, 

 but was quite incapable of transmitting the human voice with 

 its innumerable modulations of sounds, varying both in period and 

 intensity. 



These defects in the instrument of Reiss have been remedied by 

 Mr. Edison, who, by establishing contacts through the medium of 

 powdered plumbago, has succeeded in transmitting galvanic cur- 

 rents varying in intensity with the amount of vibration of the 

 diaphragm. 



As another step towards the accomplishment of the perfect 

 transmission of sound, I should mention also the logograph, or 

 recorder of the human voice, which Mr. William Henry Barlow, 

 F.R.S., a member of our Society, communicated in a paper to the 

 Royal Society, on the 23rd February, 1874. 



In adding a contact arrangement to the recording pencil of 

 Mr. Barlow's instrument, the message could obviously be trans- 

 mitted to a distance to be recorded there either by graphical or 

 audible signals. 



The beautifully simple instrument of Professor Graham Bell, 

 of Cambridge, U.S., must be regarded as a vast step in advance of 

 all previous attempts in the same direction. In making the dia- 

 phragm of iron, and having recourse to Faraday's great discovery 

 of magneto-induction, Mr. Bell has been able to dispense with the 

 complication of electrical contacts and batteries, and to cause the 



