1878.] in varying the Force of an Electric Current. 367 



the mass of the conductor, and therefore in varying its electrical 

 resistance, for we reduce the length of a portion of the conductor to 

 a fraction of the length of a sonorous wave. Molecular action alone 

 explains to me all the effects produced. Size or shape does not affect 

 them. A piece of willow charcoal, the size of a pin's head, is quite 

 sufficient to reproduce articulate speech. I regard the action as 

 follows : — If we have two separate conductors joined simply by contact 

 this contact offers a certain resistance. Now we can vary or lessen 

 the resistance by increasing the pressure, thus bringing more points in 

 contact or closer proximity. Now, as I employ a constant pressure on 

 the contact, which is exactly under the same influence of the vibra- 

 tions as the points of contact, more points or closer proximity can 

 only be obtained through the molecular swelling or movement of the 

 contact points. 



If we assume a line of molecules at the point of contact of the 

 minute masses of conducting matter in their neutral condition to be 

 arranged thus : — 



they will appear thus under compression : — 



and thus under dilatation : — 



In the former case the electrical resistance would be less, and in the 

 latter case more than in the normal condition. Hence we should get 

 variation in their electrical resistance, and thus sonorous waves could 

 vary the strength of an electric current, and the variations of the 

 electric current can be made to reproduce sonorous vibrations. These, 

 however, would only produce the result in a certain line, say horizontal; 

 but those perpendicular, while producing the same result, would be a 

 half vibration behind, and thus if two contacts, the one horizontal and 

 the other perpendicular, were on the same piece of charcoal and the 

 conducting line joined to both, we should have interference. The 

 contrary takes place as the more contacts we have, and the more 

 varied their direction on the same, the louder and purer the sound 

 becomes. Hence there is no interference, and consequently the whole 

 mass must swell and diminish equally in all directions at the same 

 instant of time. 



The tube transmitter, which I exhibit this evening, consists of an 

 exterior glass tube two inches long and one quarter of an inch in 



