1914] on Improvements in Long-Distance Telephony 85 



enters, there are special difficulties in telephonic transmission which 

 are introduced bj the line or cable. It is to these that we shall 

 devote our attention chiefly to-night, neglecting the imperfections of 

 the transmitter and receiver themselves as translating devices. 



This does not imply that the latter are unimportant, for indeed 

 there is still great room for invention to overcome their present 

 defects, but since the line or cable is the most costly element in long- 

 distance telephony any improvement in its speech-transmitting powers 

 is of the utmost importance. 



If time permit, a few words may be said on the inventions which 

 may enable the line in some cases to be entirely abolished. 



It will be useful to mention first the means at our disposal for 

 studying the changes of air pressure made near the transmitter and 

 those of the current into the line. 



If we speak or sing to an ordinary phonograph, the delicate 

 chisel attached to the diaphragm of the mouth-piece cuts a groove 

 in the plastic cylinder or disc, the bottom of which is very irregular, 

 but is a copy more or less of the movements of the diaphragm. 



I have attached to a diaphragm, in place of the chisel, a small 

 lever which moves a little mirror, and I throw on to the mirror a 

 ray of light. We can thus give to the reflected ray motions corre- 

 sponding to those of the diaphragm. If the ray falls back on a 

 steadily revolving mirror, consisting of an octagonal frame bavins' 

 its sides covered with looking-glass, and thence is reflected to a 

 screen, the moving ray makes a line of light which is unbroken and 

 nearly straight if the diaphragm is not in motion. When, however, 

 we speak or sing to this artificial ear, or phonautograph, the move- 

 ment of the small mirror causes a deflection of the ray, and moulds 

 the line of light into a shape which renders the character of the air 

 pressure changes visible to the eye. 



If we sing to it a pure musical sound, the line crinkles itself 

 into a smooth undulation called a simple harmonic curve, or curve of 

 sines. If we act on it a more complex sound, such as that of a 

 harmonium reed, we find the curve becoming rippled with other 

 subsidiary undulations which give it an irregular outline, the irregu- 

 larities being repeated at equal intervals. If we speak to the dia- 

 phragm a sentence we have a non-repetitive line, and if that sentence 

 has in it certain consonantal sounds, particularly explosive consonants, 

 such as h or p, the amplitude of the undulations becomes very large 

 at some points. Thus the words — 



" To be or not to be, that is the question. 

 Whether 'tis nobler in the mind to suffer 

 The slings and arrows of outrageous fortune, 

 Or to take arms against a sea of troubles, 

 And by opposing end them ? " 



reveal themselves on our line of light by casting it into a shape 

 which suggests an outline of the Alps with its peaks and passes. 



