Steady Electric Oscillations in Closed Circuits. 673 



of 16 to 20 inches of water, to impinge upon the spark-gap. 

 An aperture is left in the cast-iron chamber, through which 

 this air escapes. By using a small spark-gap not more than 



s 



a 



a 



s 



LLJ 



i r 



Fig. 1. — Transmitting Circuits. 

 3 mm. in length, and a suitable pressure of air, it is possible 

 to maintain oscillations of great constancy in a circuit which 

 includes the spark-gap S, a suitable condenser Ci, and the 

 closed circuit L x which constitutes the radiator. The radiator 

 is preferably made by winding 8 or 10 turns of stranded 

 insulated wire upon a square wooden frame, which may be 

 anything from 2 feet to 8 or 10 feet in side. The condenser 

 may be an ordinary leyden-jar, or preferably an oil-con- 

 denser consisting of metal plates placed in anhydrous paraffin 

 oil. The high-frequency capacity of this condenser can then 

 be measured accurately, and also the inductance of the 

 radiative circuit and the frequency of the sparks can be 

 ascertained by a spark-counter, as described previously by 

 one of us. The mean-square value of the current in the 

 oscillatory circuit can be determined by a hot-wire or thermo- 

 electric ammeter inserted in it, or in a circuit M inductively 

 coupled to it, and it will be found that if the above arrange- 

 ments are adopted, the mean square value of the discharge 

 current in the oscillatory circuit can be kept extremely constant 

 for hours together. Signals can also be automatically sent 

 by interrupting the primary circuit of the transformer or 

 induction-coil by a key operated by a punched tape. In 

 Phil. Mag. S. 6. Vol. 17. No. 101. May 1909. 2 Z 



