64 POPULAR SCIENCE MONTHLY. 



denser and a sensitive metallic filings tube of the Branly type; also a 

 portion of this resonant circuit is shunted by another consisting of a 

 battery and telegraphic relay, as shown in the diagram. The circuit, 

 including the coherer, is tuned to its own aerial and also to that of the 

 transmitting circuit, and under these circumstances trains of waves 

 thrown off at the transmitting aerial will sympathetically affect the re- 

 ceiving aerial. 



There is nothing in the arrangement which specially calls for 

 notice. It is simply a variation of other known forms of syntonic 

 transmitter and receiver, and possesses all the advantages and disad- 

 vantages attaching to such electrical syntonic methods. 



Professor Braun's syntonic system, the receiver and transmitter of 

 which have been described, is also in one form a non-earthed system. 

 Innumerable other patentees have taken out patents for devices which 

 are modifications in small degree of the above arrangements. 



It may be well to note at this point the disadvantages that are 

 possessed by any form of coherer as a telegraphic kumascope in con- 

 nection with proposed arrangements for the isolation of Hertzian wave 

 stations. All the detectors of the coherer type really depend for their 

 actuation upon electromotive force; that is to say, upon the applica- 

 tion to the terminals of the detector of a certain electromotive force. 

 Although there may be no sharp and defined critical electromotive 

 force, yet, nevertheless, as a matter of fact, if the electromotive force 

 applied exceeds a certain value, then the detector passes suddenly from 

 one state of conductivity to another. It may be of great conductivity, 

 as in the case of the Branly coherer, or of lesser conductivity, as in the 

 case of the so-called anticoherers, of which the Schafer kumascope 

 may be taken as a type. Accordingly, when these instruments are 

 subjected to a train of waves, each individual group of which is 

 damped, their operation is largely governed by the fact that if the first 

 wave or oscillation set up in the receiving circuit is powerful enough 

 to break down the coherer, then the receiving mechanism acts, no 

 matter whether the first impulse is followed by others or not. 



In comparison with so-called coherers, those depending upon the 

 changes in the magnetization of iron by electrical oscillations cer- 

 tainly have an advantage, because this is a process which requires 

 the application of alternating electric currents decreasing in strength 

 for a certain time; and it is found therefore that the magnetic re- 

 ceivers do not require to be associated with such a stiff or irresponsive 

 resonant circuit to confine their indications to oscillations or waves of 

 one definite period, and that they lend themselves much more perfectly 

 to the work of 'tuning' or syntonizing stations than do those kuma- 

 scopes depending upon the contact or coherer principle. 



We may then glance at the alternative solutions of the problem 

 offered by other investigators. M. Blondel has proposed to effect the 



