Prof. W. Siemens on Telephony. 93 



As *to the relative evidence for the two figures presented 

 in this paper, the sum of the squares of the residual cor- 

 rections to the astronomical observations is, of course, less 

 in the ellipsoid than in the spheroid ; but the difference is cer- 

 tainly small. The radius of curvature perpendicular to the 

 meridian in India, in latitude 15° say, is, on the spheroid, 

 20930972 feet, whereas on the ellipsoid it is 20932877 ; and 

 this last is distinctly more in harmony with the Indian Lon- 

 gitude Observations. 



Ordnance Survey Office, Southampton, 

 June 15, 1878. 



XIII. On Telephony. By W. Siemens *. 



THE surprising performances of the telephones of Bell and 

 Edison rightly claim in a high degree the interest of 

 natural philosophers. The solution (facilitated by it) of the 

 problem of the conveyance of tones and the sounds of speech 

 to distant places promises to give mankind a new means of 

 intercourse and culture which will essentially affect their social 

 relations and also render substantial service to science ; and 

 hence it seems fitting that the Academy should draw these 

 exceedingly promising discoveries into the sphere of its contem- 

 plations. 



The possibility of reproducing mechanically not merely 

 tones, but also noises and spoken sounds, at great distances is 

 given theoretically by Helmholtz's path-opening investiga- 

 tions, which elucidated the essential nature of shades of tone 

 and the sounds of speech. 



If, as he has demonstrated, noises and sounds are only distin- 

 guished from pure tones by the fact that the latter consist of 

 simple, the former of a plurality of series of undulations, super- 

 posed to one another, of the sonorific medium, and if the noises 

 of speech (Sprachgerausche) may be conceived as irregular vi- 

 brations with which the vocal sounds begin or end, then it is 

 also possible to reproduce mechanically a certain succession of 

 such vibrations at distant localities. Indeed practical life has 

 in this, as is frequently the case, outrun science. The hitherto 

 too little regarded so-called " speaking telegraph," consisting 

 of two membranes stretched by a strong and at the same time 

 extremely light thread or fine wire which is fastened to their 

 centres, effects a perfectly distinct transmission of speech to a 

 distance of several hundred metres. The threads or wires can 



* Translated from the Monatsbericht der koniglich preussischen Aha- 

 demie der Wissenschaften zu Berlin, January 1878, pp. 38-53. 



