Prof. W. Siemens on Telephony. ' 99 



It follows from the above that Bell's telephone, notwith- 

 standing its surprising performances, effects the conveyance 

 of sound only in a very imperfect manner. That we can 

 understand the speech of the telephone excited by currents so 

 extraordinarily feeble, we owe to the extreme sensibility and 

 great range of our organ of hearing, which enable it to bear 

 the sound of a cannon at 5 metres distance, and yet to hear it 

 at a distance of 50 kilometres, consequently to have the sen- 

 sation of sound from air-vibrations within a range of from 1 

 to 100,000,000-fold intensity. 



Accordingly the telephone needs, and is in a high degree 

 capable of, improvement. Although it is not possible entirely 

 to do away with loss of sound (which would be approximately 

 accomplished if it could be effected that the vibrations of the 

 second membrane should possess the same amplitude as those 

 of the first), since in the repeated transformations of motions 

 and forces there must always be a loss of vis viva by conver- 

 sion into heat, yet the present disproportion is much too great. 

 But by diminishing this loss, and thereby strengthening the 

 arriving sound, we should secure that the hearing would need 

 less exertion, and could distinctly perceive and distinguish the 

 transmitted sounds at a greater distance from the instrument. 

 Then also the perturbations produced by extraneous feeble 

 electric currents would be felt less disturbing, because they 

 would be covered by the more powerful arriving speech- 

 sounds. 



Hereby is also given the direction which must be taken for 

 the improvement of Bell's telephone. In order to produce 

 more intense currents, the membrane destined to receive the 

 sound-waves must be sufficiently large and of such a consti- 

 tution that the sound-waves striking its surface can impart to 

 it a maximum of their vis viva : while the membrane must be 

 sufficiently movable for its vibrations not to be too small : and 

 the work expended for the production of the electric currents 

 must be so much that the vis viva accumulated in the vibra- 

 tions of the membrane will be consumed by it — or, in other 

 words, so much as to make the membrane-vibrations aperiodic. 

 An enlargement of Bell's iron sheet would be advantageous 

 only within narrow limits, since larger and correspondingly 

 thicker plates are apt to assume vibrations of their own, which 

 diminish the distinctness of the transmitted sounds. It is also 

 requisite that the magnetic attraction of the iron plate in Bell's 

 telephone be not raised too high, as otherwise the plate is too 

 much curved and stretched in one direction, which likewise 

 detracts from the clearness. 



I have tried, with considerable success, to strengthen the 



H2 



