Rormell — Dielectric Constant of Paraffins. 441 



Let us suppose that the oscillator is adjusted for a half wave 

 length of about 40 cm . Take a block of paraffin 40 cm long, 6 cm 

 wide and 8 cm thick. It can be readily sawed from a commer- 

 cial cake by means of a table rip-saw. With this same saw 

 make two grooves l'8 cm apart and half way through one side. 

 Bring the block up under the two Lecher wires, making them 

 lie in the grooves and placing the end of the block against the 

 support of the first bridge. Using a hot iron and a piece of 

 paraffin, run the melted wax into the grooves, thus making a 

 solid column around the wires. Place the argon tube between 

 the free end of the column of wax and the movable bridge. 

 When the oscillator is in action and the tube located, it will be 

 noticed that the distance between the end of the column and 

 the bridge is less than the half tube wave. The column may 

 now be cut off piece by piece until the wire node of the half 

 tube wave rests on the end of the column. The length of the 

 column plus half the distance between the Lecher wires (*9 cm ) 

 is very approximately the half wave length in paraffin. In the 

 actual experiment the length of this column was 26'4 cm . And 

 if to this we add *9 cm we shall get 27'3 cm as the approximate 

 wave length. If the base of the apparatus be long enough for 

 three half waves, a column of paraffin 85 or 90 cm long ought to 

 be moulded. For this purpose a box was prepared 90 cm long, 

 8 cm wide, and 8 cm deep, and was lined with tinfoil. It was 

 put together with screws so that it could be easily taken apart. 

 By a suitable contrivance two copper wires l'8 cm apart could 

 be stretched through the middle of the box and made long 

 enough to be fastened in the two supports of the base. The 

 melted paraffin was poured into the box and allowed to cool 

 partially. Then a closely fitting top was placed on the paraf- 

 fin and the whole subjected to a pressure brought into play by 

 three iron clamps. A gauge inserted in the side of the box 

 recorded the pressure. All this was necessary in order to 

 secure columns uniformly dense and free from air holes. 

 Having a column thus suitably prepared, one must decide two 

 questions before a final determination of the dielectric constant 

 is made. 



1st. How much beyond a node may the end of the paraffin 

 column rest without changing the position of the second 

 bridge ? 



2d. How large in area must the section of the column be 

 in order to include the whole of the effective field surround- 

 ing the Lecher wires ? 



The first question can be quickly answered. Fasten the 

 moulded column between the supports, making one end rest 

 against the first support. It will be about 3 mm from the first 

 bridge, since the bridge rests in a groove 3 mm from the outer 



