98 Prof. W. Siemens on Telephony. 



metres long very distinctly ; it was still audible when the ear 

 was withdrawn 8 centims. from the mouth of the hearing- 

 tube. The ticking could be heard direct with about equal 

 distinctness at the distance of 130 centims. ; consequently 

 the thread telephone conveyed about ^Jo °f ^ ne intensity of 

 the sound. Since the electric telephone transmitted the softest 

 speech intelligibly, it must be on account of the rapid and ir- 

 regular vibrations which form the toneless, even if louder, 

 noise of the ticking, that it cannot transmit the latter. 



From a like cause a proper, perfectly toneless whisper 

 cannot be understood through the electric telephone, while 

 through the thread telephone it is distinctly intelligible to a 

 distance of 20 metres. Just so electric telephones, which re- 

 produce the softest speech distinctly, do not convey at all, or 

 scarcely perceptibly, the loud but toneless clap of two pieces 

 of iron or glass struck together. 



It is remarkable that the electric telephone, in spite of this 

 almost incapability of conveying the noises which consist of 

 rapid and irregular vibrations, yet so truly renders the quality 

 of musical tones and the sounds of speech that the voices of 

 the speakers can be almost as well recognized through the 

 telephone as direct from the speakers themselves. The voice, 

 however, sounds somewhat fuller, which is to be ascribed to 

 the circumstance that the tones are reproduced better and 

 more powerfully than the noises of speech. Singing, too, 

 sounds through the telephone, as a rule, softer and richer. 



In order to gain a fixed point for the solution of the ques- 

 tion what fraction of the force of the sound which strikes the 

 membrane of the one telephone is given again by the other, I 

 instituted some experiments with musical boxes. The smaller 

 one, which gave short sharp tones, could be heard by good 

 ears at 125 metres distance upon an open plain, while only 

 isolated tones could be heard through the telephone when it 

 was placed more than 0*2 of a metre from the musical box. 

 In this instance, therefore, only about 3-9^000 °^ ^ ne soun d 

 was actually conveyed. A somewhat larger musical box, of 

 not so high a pitch, and giving tones of longer duration, 

 could not be heard in the open air much further than the 

 smaller one ; but the telephone at 1*2 metre distance caused 

 the tune played to be recognized. This gives a conveyance of 

 about xocroo of the sound-intensity received by the telephone. 

 Now, although the sounds of speech, as well as deeper and 

 more sustained tones, are probably conveyed better than the 

 melody of the musical boxes, it cannot be assumed that a 

 Bell telephone conveys, on the average, more than toooo °^ 

 the mass of sound by which it is struck, to the other telephone. 



