Hormell — Dielectric Constant of Paraffins. 435 



the control of the observer. The two semicircles comprising 

 the primary coil are firmly fastened to two hard rubber 

 uprights which are pivoted on the crossbar L. 



The screw D regulates the spark gap m. A spiral spring, 

 not shown in the figure, wound round D, keeps the two 

 uprights separated. The wire E' is passed through a thick- 

 walled glass tube and is inserted in one of the ball terminals 

 of the primary. The other wire E forms a spark gap at &, 

 which is regulated by the screw G. The glass tubes are held 

 in place by pressure screws not shown in the figure. This 

 framework holding the primary is placed in a 4x5 in. glass 

 jar. Immediately under the primary a secondary of the same 



diameter is placed, and its terminals are led out through two 

 corks inserted in the side of the jar (figure 3). This coil is 

 firmly held in position by three rubber posts sent up from a 

 rubber plate placed in the bottom of the jar. A mica plate is 

 placed between the primary and secondary, the distance 

 between which is regulated by the screw A (figure 2). The 

 screw-clamp F (figure 3) holds the framework of the primary 

 rigidly in place. When the coils are in use the jar is filled 

 with kerosene. 



The first bridge, B 1 (figure 3), rests in a groove in the rubber 

 support. It is 30 mm long, l mm thick and 3 mm wide. It has two 

 holes in which to receive the ends of the secondary, and these 

 when in place are soldered to the bridge. Two grooves sym- 

 metrically placed are filed on top of the bridge, l'8 cm apart. 

 The Lecher wires, L, rest in these grooves and are clamped 

 firmly to the bridge by means of the top of the rubber sup- 

 port, which is furnished with two strong brass screws. The 

 other ends of the Lecher wires, l*8 cm apart, are clamped in a 

 second rubber support. The supports, about 150 cm apart, are 

 strong enough to allow a tension of several pounds on the 

 wires. Unless otherwise designated, the Lecher wires are 

 made of 2s"o. 18 copper wire. 



The second and movable bridge, B 2 , is a brass wire l mm in 

 diameter and 4 cm long. The post holding the bridge works in 

 a socket containing a spring which presses the bridge against 

 the two wires. The base of the bridge holder has an index 



