Dielectric Constants by means of Hertz Oscillations. 177 



Glass. — If a glass plate 0*8797 centim. thick was placed 

 between the condenser-plates I obtained, corresponding to 

 distances between the plates of 1*582 and 1*954 centim., for a, 

 the positions 634*57 and 587*54 centim. ; and corresponding to 

 1*954 centim., I found for c the position 1042*74 centim. 



These numbers were used in the same manner as the 

 previous ones. The distance apart of the condenser-disks 

 differs, according as the glass is inserted or not, by 0*758, 

 0*767, and 0*753 centim. The value of the dielectric con- 

 stant is found to be 7*31. 



Petroleum. — In order to bring a layer of liquid between 

 the condenser-plates, I took a wooden ring whose internal 

 diameter was 14 centim. On each face was fastened a thin 

 glass plate, and thus a disk-shaped space was formed for the 

 reception of the liquid. The thickness of the whole system 

 was measured in thirty places, the liquid having been first 

 inserted, in order to take account of the bulging produced 

 by the pressure of the liquid against the sides of the vessel. 

 The thickness of the two glass plates had also been previously 

 measured in thirty places before cementing them on the ring. 

 From these data the thickness of the liquid film could be 

 calculated exactly. 



If the two glass plates 0*4338 centim. thick were inserted 

 between the condenser-plates, separated 1*590 centim., the 

 ventral segment a was situated 583*93 centim. from the end 

 of the wire ; the same ventral segment corresponds to an air- 

 condenser of 1*223 centim. thickness. The difference was 

 0*367. We obtain thus for the dielectric constant of the 

 glass used (" Solinglas ") 6*50, which number, however, may 

 be less accurate than the others given in this paper, because 

 the glass plates were too thin. 



In order to obtain the dielectric constant of petroleum, I 

 next found 571*93 for the ventral segment when petroleum 

 and two glass disks were between the condenser-plates, these 

 latter being separated by a distance of 2*848 centim. For 

 the same ventral segment an air-condenser of thickness 1*348 

 centim. was required. The difference of these numbers 1*500 

 must be reduced by 0*367, which number, as shown above, 

 expresses the effect of the two glass disks. After taking away 

 the layer of petroleum alone, whose thickness was 1*9272 

 centim. (the glass disk still remaining in position), I had to 

 diminish the distance apart of the condenser-plates by 1*133 

 centim. to make its capacity the same as before ; and thus I 

 obtain the value 2*42 as the dielectric constant of petroleum. 



The petroleum used was the common commercial liquid as 

 used for burning, and contained some water. 



