196 THE SCIENTIFIC PAPERS OF 



In the discussion of the Lecture 



"ON THE CONNECTION BETWEEN SOUND AND 

 ELECTRICITY," by ME. W. H. PREECE, 



The PRESIDENT * (Mr. C. W. Siemens), said, as time is advanc- 

 ing, and as Mr. Preece, I believe, has some further experiments, 

 to exhibit at the close of the meeting, I will make a few observa- 

 tions only on the very interesting matter which has been brought 

 before us. The discussion that has taken place is remarkable 

 for the excellent temper v which has been shown by two great 

 rival discoverers. I think all of us must have been pleased to 

 have seen how these two gentlemen, Professor Bell and Professor 

 Hughes, have described and brought before us their particular 

 views regarding certain actions in the two instruments, the tele- 

 phone and microphone, which, when we come to compare them, 

 will be found to have many points of analogy, and though essenti- 

 ally different in detail, tend towards the accomplishment of the 

 same important end. Mr. Preece and Professor Bell differ with 

 regard to the action which takes place in the microphone, and 

 Professor Hughes favours naturally the views which Mr. Preece 

 has expressed ; but I think there is probably not so much differ- 

 ence between those two views. It is quite evident that the action 

 of the microphone is due to variation in electrical resistance pro- 

 duced by vibrations in an imperfect conductor, such as carbon, or 

 an aggregate of divided pieces of metal, and the question for con- 

 sideration is how this variation in resistance is effected. When 

 two pieces of carbon are pressing one upon the other, and vibra- 

 tion is imparted to one of them, it is easily conceived that in 

 consequence of this vibration the pressure between the adjoining 

 points of the carbon will be modified, and in consequence of such 

 variation in pressure, the electric conductivity of the carbon is 

 also influenced, whilst according to Professor Hughes's explanation, 

 the cause of variations in the electrical resistance must be looked 

 for in the lateral increase of points of contact. 



* Excerpt Journal of the Society of Telegraph Engineers, Vol. VII. 1878, pp. 

 290-292. 



