300 A Detector for Spark in Hertz's Resonator. 



spiral spring S. To allow for this adjustment P is bent as 

 shown, and P ; , though fixed permanently, is also bent, so 

 that both parts of the resonator may be symmetrical. With 

 this arrangement one pair of resonator wires can be very 

 readily replaced by another pair of a different size. 



A Detector for Spark in Hertz's Resonator. 



T is a glass tube open at the top. Its lower end is closed 

 and two platinum electrodes E are sealed into it. Two small 

 holes are bored through it diametrically opposite to each 

 other, through which the platinum wires P and P ; can pass 

 freely. This tube is partly rilled with hydrochloric acid, and 

 the electrodes E are connected with a battery so as to generate 

 an explosive mixture of hydrogen and chlorine. If the 

 resonator sparks when enough gas is present in the tube, an 

 explosion is produced. 



In order that an explosion may be produced by every 

 spark, the time required to fill the tube with the quantity of 

 gas requisite for an explosion must be less than the interval 

 of time between two sparks. If this interval is small, the 

 quantity of gas requisite for an explosion must be small and 

 it must be generated quickly. Now in order that the quantity 

 of gas requisite for an explosion may be small, the diameter 

 of the tube must be small and the spark-gap must be near the 

 surface of the electrolyte. We find, however, that when 

 under these circumstances the gas is generated quickly, an 



