312 



SCIENCE. 



applying one ear to the 

 knob of the jar. Every 

 word spoken at thetrans- 

 mitter was distinctly 

 heard, but the prickly 

 sensation due to the el- 

 ectricity was too dis- 

 agreeable. Another re- 

 ceiver, not less curious 

 than the Leydenjar, was 

 found in the pair of insu- 

 lating handles made for 

 the medical application 

 of electricity. When 

 these were connected to 

 the coil wires, and one 

 held in each hand by 

 the wooden part, while 

 the metallic ends were 

 placed at the ears, any 

 kind of a sound at the 

 transmitter was heard 

 without any difficulty, 

 but of course the same 

 sensation was felt as 

 with the jar. Many forms 

 of condensers have been 

 employed with capacities 

 too small to measure up 

 to two micro-farads, and these in all sorts of relations, 

 charging the plates from batteries, from Holtz machines, 

 charging the line as in cable works, etc., all of which give 

 results that differ only in degree. 



THE TRANSMITTER. 



As with other systems in common use, there is 

 a transmitter as well as a receiver. One form of 

 the transmitter is attached to the door of a box 

 containing battery and 

 coil. This transmitter 

 is substantially the 

 same as the one in- 

 vented by Rtiss in 

 1861. His consisted of 

 a cubical box (see Fig. 

 6) about five inches 

 on a side, having an 

 opening on one side 

 to talk into, and an- 

 other one on top, across 

 which the diaphragm 

 was fastened. A pin 

 of platinum was glued 

 to the middle of the 

 membrane, and con- 

 nected by a wire to 

 a binding screw. A 

 V-shaped wire with 

 platinum point touch- 

 ed upon the platinum 

 of the membrane, and 

 with its binding screw 

 served to complete a 

 galvanic circuit. This 

 one (see Fig. 10) differs 

 from this of Reiss only 

 in making the chamber 

 smaller, making the 

 connecting wire on top 

 T-shaped, and substi- 

 tuting carbon or other 

 suitable substance for 

 the platinum ; but the 



Figure G. 



platinum does very well. 

 It is a matter of some 

 surprise that the old 

 transmitter is still spok- 

 en of as a make and 

 break circuit, and that it 

 can only transmit pitch, 

 whereas, whether it 

 breaks or not when a 

 sound is made in it de- 

 pends solely upon the 

 intensity of that sound, 

 just as with the Blake 

 transmitter, if one talks 

 gently to the original 

 Reiss transmitter, it not 

 only does not break, but 

 it transmits speech with 

 all its qualities. 



Accompanying the 

 transmitter an induc- 

 tion coil is shown at I, 

 Fig. 6, and as the work- 

 ing of the receiver de- 

 pends upon electromo- 

 tive force and not upon 

 current, it is necessary, 

 if a coil be used to raise 

 the electromotive force, 

 to have one with many more turns than is needed 

 with the magneto receiver, and the best results have 

 been obtained with a coil having a resistance of four or 

 five thousand ohms, but it is probable that this will be re- 

 duced. 



On account of the high electromotive force a better in- 

 sulation is needed than ordinary telegraph lines give, 

 when the induction coil is at the further end of the line, 

 but if it is at the receiving end, and a low electromotive 



force is employed in 

 the primary, then or- 

 dinary insulation will 

 answer. Again, the 

 electromotive force be- 

 ing high, inserted re- 

 sistances do not so 

 markedly decrease the 

 efficiency of the instru- 

 ment, as in the case 

 with the magneto-tel- 

 phone. For instance, 

 the articulation is per- 

 fect and loud enough 

 with a resistance of 

 fifty thousand ohms, 

 a resistance equal to 

 five thousand miles ot 

 common telegraph 

 wire, and it may be 

 heard through a re- 

 sistance of a million 

 ohms, practically an 

 infinite resistance. 



If one of the termi- 

 nals of a receiver be 

 charged in any way, 

 the reaction between 

 the two plates will be 

 stronger than it will be 

 without. Let, then, 

 one terminal be at- 

 tached to a knob of a 

 Holtz machine that is 

 |& kept charged by rota- 



FlGUKE 7. 



