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SCIENCE. 



DOLBEAR'S NEW TELEPHONE SYSTEM. 



Among the exhibits at the forthcoming International 

 Electrical Exhibition at Paris, the new telephone we are 

 about to describe will command attention as an original 

 and important invention. 



It embodies the most recent discoveries of Professor 

 A. E. Dolbear, of Tuft's College, Massachusetts, who,' 

 as one of our most esteemed contributors, needs no in- 

 troduction to the readers of " Science." 



The advantages claimed by Professor Dolbear may be 

 summarized as follows : 



1. It is a new and independent system which has im- 

 portant advantages over the Bell and other Telephonic 

 methods. 



2. Its capability of transmitting speech over longer 

 lines of wires than has been hitherto employed, and its 

 freedom from the troubles of induction. 



3. It is a silent instrument, the words coming out 

 clear without the sputtering aud confused noises of the 

 old system. 



4. It is an absolute departure from the Bell system, 

 and its principles of operation entirely independent. 



We are enabled to place before our readers a descrip- 

 tion of this original telephone prepared by Professor 

 Dolbear himself, illustrated by some excellent cuts loaned 

 to us by Mr. H. C. Buck, who is leaving for Paris to 

 represent Professor Dolbear at the forthcoming Electrical 

 Exhibition. 



Before describing Professor Dolbear's Telephone in 

 detail, we may state that in order to receive messages by 

 the Bell system it is necessary to use between the ear and 

 the line wire an electrical machine, consisting of a magnet, 

 a magneto-coil to influence the magnet, which coil is con- 

 nected with the line wire and with the ground. Take out 

 this machine, and we take out the Bell telephone system — 

 this is substantially what Professor Dolbear claims to do 

 — for to receive a message, he takes out the machine, and 

 puts the end of the telegraph wire directly to the ear. 

 For convenience of ordinary use Professor Dolbear pro- 

 vides the receiving end of his telegraph wire with a small 

 handle, in which he arranges a couple of thin diaphragms, 

 one of them attached to the wire — a contrivance that 

 improves the vocal delivery of the line wire. 



Professor Dolbear thus describes his invention : 



RECEIVER. 



This consists, in its simplest form, of two metallic 

 disks about two inches in diameter, so mounted as not to 

 be in metallic contact, and this is effected by turning a 



Figure 1. 



flange in a hard rubber case so they may be kept apart 

 by it (see Fig. 1). A cap is screwed down upon each 

 plate; one of them having a small hole in the middle of it 

 to listen at ; the other is a larger one, having a knob 

 turned upon it for conveniently holding it in the hand. 

 Through the middle of the knob a screw is sunk which 

 touches the back plate and serves to adjust it to the best 

 position relative to the front or vibrating plate. The 

 back plate is thus- fastened at both edge and middle, 

 which prevents it from vibrating, while the front plate is 

 only fast at its edge, leaving the middle free to vibrate. 



Figure 2. 



Each of these plates, A B, Fig. 2, is in metallic connec- 

 tion with the induction coil so as to be its terminals. 

 When thus connected and one makes and breaks connec- 

 tion in the primary circuit, a click may be heard by one 

 holding the receiver near to the ear. If a Helmholtz in- 

 terrupter be employed to make and break the primary 

 circuit, the pitch of the fork can easily be heard, and with 

 a Keiss transmitter or other suitable one in the same 

 place, any kind of a sound will be reproduced. 



The explanation of this is easily understood from the 

 foregoing description of the conditions present. The 

 electromotive force generated by induction in the coil 

 changes the two terminals in the receiver, one positively, 

 the other negatively ; they therefore attract each other. 



One of them is free to move, while the other is rigid. 

 The middle of the freer plate consequently moves slightly 

 toward the other whenever they are electrified, and in so 

 doi?tg. spends the energy of the electricity, while its elas- 

 ticity brings it back to its place. It is not essential, how- 

 ever, that both of these terminal plates should be con- 

 nected to the induction coil, for if only one is connected, 

 the recurring charges will cause the free plate to vibrate, 

 for a charged body will attract any other body, so if the 

 connection be to the back plate it will attract the front 

 one and make it move, and if the connection be to the 

 front plate it will attract the back plate and approach it. 

 The effect will be increased by putting the finger upon 



