130 



PHOTO-TELEGRAPHY 



shunt these with a capacity K and an inductance X, 

 and bring the spark balls P, P hear together, the 

 spark becomes very intense, and electrical oscilla- 

 tions are set up, the frequency of which is given by 

 the expression 



n = 



where n is the frequency and L is the inductance 



FIG. 58. 



measured in centimetres, and C the capacity in 

 microfarads. 



If now we use the inductance X as the primary of 

 a small transformer, and the secondary Y is placed 

 between a connection to earth E and the aerial wire 

 or wires of the antenna A, and the oscillation fre- 

 quency of the aerial circuit tuned to that of the 

 spark gap circuit, we have a transmitting station 



