HERTZIAN WAVE WIRELESS TELEGRAPHY. 



113 



discharges it through a galvanometer. If this galvanometer is sub- 

 sequently standardized, so that the ampere value of its deflection is 

 known, we can determine easily the capacity C of the aerial or insu- 

 lated conductor, reckoned in microfarads, when it is charged to a 

 potential of V volts, and discharged n times a second through a 

 galvanometer. The series of discharges are equivalent to a current, of 

 which the value in amperes A is given by the equation. 



A 



nVC 

 10" 



and hence if the value of the current resulting is known, we have the 

 capacity of the aerial or conductor expressed in microfarads, given by 

 the formula, 



AlO^ 



C= 



nV 



A series of experiments made on this plan have revealed the fact 

 that if a number of vertical insulated wires are hung up in the air 

 and rather near together, the electrical capacity of the whole of the 

 wires in parallel is not nearly equal to the sum of their individual 

 capacities. If a number of parallel insulated wires are separated by 

 a distance equal to about 3 per cent, of their length, the capacity of 

 the whole lot together varies roughly as the square root of their num- 

 ber. Thus, if we call the capacity of one vertical wire in free space, 

 unity, then the capacity of four wires placed rather near together will 

 only be about twice that of one wire, and that of twenty-five wires will-Y'?.- 

 onlv be about five times one wire. 



M 



1 W 



V 







Fig. 8. Various forms of Aerial Radiator. 

 Shape ; d Cylindrical ; g, Conical. 



a, Single Wire ; b, Multiple Wire ; c, Fan 



This approximate rule has been confirmed by experiments made 

 with long wires one hundred or two hundred feet in length in the 

 open air. Hence it points to the fact that the ordinary plan of 

 endeavoring to obtain a large capacity by putting several wires in 

 parallel and not very far apart is very uneconomical in material. The 

 diagrams in Fig. 8 show the various methods which have been employed 



VOL. LXIII. 8. 



