STATIC ELECTRICITY 



liquid to be examined. The principle of the method may be 

 gathered from Fig. 88. 



J was an induction coil connected by wires A A to the terminals 

 of the Blondlot exciter E E, which consisted of two semicircle 

 with diameter in some cases 5 cm. and in other cases 15 cm. 

 The brass terminals of E E were 5 mm. diameter, and the spark 

 gap between them could be varied by a micrometer. Hound E E 

 was a circular wire continued by the parallel wires D D about 

 2 cm. apart. These might be continued, when desired, into a 

 trough containing the liquid to be tested and from 150 cm. to 

 60cm. long. When sparks took place across the gap in E V. ua\< - 

 were propagated in the space between D D with the velocity <>t 

 free waves. U 1 H 2 were holders to keep the wires adjusted and 

 Bj and B 2 were two wire bridges. Between these, stationary 

 waves were formed. B x was adjusted to be at the first node; the 

 second node was where the wires entered the trough of liquid, 





FIG. 88. J induction coil ; A A wires from its terminals to the exciting circuit 

 E E, round which is a circuit prolonged by the two wires D D ; fy B a bridge*, 

 B! fixed, B 2 in the liquid trough movable ; Z Xehnder vacuum MM Hffctin| 

 up at a loop. 



and B 2 was moved about till it was at a third or further n- 

 In the original arrangement Z was a vacuum tube with terminals 

 connected by a wire s of such length that the electrical period of 

 the tube coincided with that of the exciter, but a neon tube laid 

 across the wires suffices. When B, was at a node and Z at a loop. / 

 lighted up with maximum brilliance. Several successive nodal 

 positions were observed by means of this maximum brilliance, and 

 these were, of course, at intervals of X t /SJ. Then the trough 

 detached and replaced by a continuation of the wires in air. 

 Nodal positions of B 2 were again observed, and thus X x /2 in air 

 was found. Thence y u = X 1 /X 2 was known. 



With this apparatus Drude was able to show the existence of 

 dispersion that is, a difference of velocity with difference of 

 frequency. He used two frequencies, respectively 150x10* and 

 400 xlO 6 . The velocity for water was practically the same for 

 both frequencies, but for glycerine /x 2 = 39*l for the former and 

 /x 2 = 25*4 for the latter, and for other liquids there were consider- 

 able differences. He found that for water at t C. the value 



