70 POPULAR SCIENCE MONTHLY. 



or oscillations — is a bar to the efforts to make -wireless telegraphy 

 secret. We can see from the photograj)!! how much greater its 

 strength is than that of the subsequent discharges shown by the 

 mere brightening of the terminals. A delicate coherer will imme- 

 diately respond to the influence of this pilot spark, and the subse- 

 quent oscillations of this discharge will have little effect. How, 

 then, can we eff'ectively time a receiving circuit so that it will 

 respond to only one sending station? We can not d(>pend upon the 

 oscillatory nature of the spark, or adopt, in other words, its rate of 

 vibration and form a coherer with the same rate. 



It seems as if it would be necessary to invent some method of 

 sending pilot sparks at a high and definite rate of vibration, and 

 of employing coherers whicli will only respond to definite power- 

 ful rates of magnetic pulsation. Various attempts have been made 

 to produce by mechanical means powerful electric surgings, but 

 they have been unsuccessful. Both high electro-motive force and 

 strength of current are needed. These can be obtained by the 

 employment of a great number of storage cells. The discharge 

 from a large number of these cells, however, is not suitable for 

 the purpose of wireless telegraphy, although it may possess the 

 ([ualifications of both high electrical pressure and strength of 

 current. 



The only a])])aratus we have at command to produce quick blows 

 on the ether is the Euhmkorf coil. This coil, I have said, has 

 been in all our physical cabinets for fifty years. It contained within 

 itself the germ of the telephone transmitter and the method of wire- 

 less telegraphy, unrecognized until the present. In its elements 

 it consists, as we have seen, of two electrical circuits, placed near 

 each other, entirely unconnected, A battery is connected with 

 one of these circuits, and any change in the strength of the elec- 

 trical current gives a blow to the ether or medium between the 

 two circuits. A quick stopping of the electrical current gives the 

 strongest impulse to the ether, which is taken up by the neighbor- 

 ing circuit. For the past fifty years very little advance has been 

 made in the method of giving strong electrical impulses to the 

 medium of space. It is accomplished simply by a mechanical break- 

 ing of the connection to the battery, either by a revolving wheel 

 with suitable projections, or by a vibrating point. All the various 

 forms of mechanical breaks are inefficient. They do not give quick 

 and uniform breaks. Latterly, hopes have been excited by the 

 discovery of a chemical break, called the Weynelt interrupter, 

 shown in Fig. 1. The electrical current in passing through a vessel 

 of diluted sulphuric acid from a point of ])latinum to a disk of lead 

 causes bubbles of gas which form a harrier to its passage whicli is 



