Refraction for Electric Waves. 183 



suffers a phase-retardation over the direct wave. This retar- 

 dation can be varied by moving the reflector backward or 

 forward, and the resultant intensity at R is measured by the 

 deflexion of the instrument. The curve obtained by plotting 

 these deflexions against the respective distances of the reflector 

 from the oscillator is a diagram of the stationary wave. 



Fig. 4. 



R 



oi 



Y. 



2 



?Wr 



V-- 1 



M 



In order not to distort the reflected wave, the oscillator, 

 which intervenes between the reflector and resonator, had to 

 be mounted in a manner somewhat different from the arrange- 

 ment described in the previous paper. The vessel for holding 

 the oil about the spark-gap was dispensed with, and the small 

 thermometer-tubes (T, fig. 5), in which the terminals were 

 fused, were mounted alone in a framework of wood. The lower 

 terminal was fastened rigidly ; while the upper one could be 

 moved up and down and twisted sideways by micrometer- 

 screws, K, so as to adjust and align the terminals. Care 

 was taken to make the framework rigid. In order now 

 for the spark to pass in a liquid dielectric, oil from a 

 reservoir above, r, is allowed to trickle slowly down the sides 

 of the tubes and over the spark, which it covers with an 

 adhering drop. With this mounting it is possible to move 

 the reflecting surface to within a few millim. of the spark, 

 permitting exploration in the immediate neighbourhood of the 

 oscillator, and it also happens that the continual renewing 

 of the oil by this arrangement gives larger and steadier 

 readings than those obtained with the old mounting. 



