Dielectric Constants by means of I Fertz Oscillations. 17 5 



1800 adjustments which I have made altogether, there 

 occurred on three occasions only a deviation from the mean 

 value amounting to 5 centim.* 



From these numbers 1 drew three curves, and endeavoured 

 to firing the new ventral segment after the insertion of the 

 substance under investigation within the limits just found, 

 this being easily accomplished by suitably altering the dis- 

 tance between the condenser-plates. 



Ebonite. — If a plate of ebonite, 0*7164 centim. thick, was 

 placed between the condenser-plates, 1 obtained, corresponding 

 to distances between the condenser-plates of 1*200 and 1*70 L 

 centim. respectively, for the ventral segment a the values 

 641*63 and 585'40 centim.; and for the ventral segment** 

 corresponding to 1*701 centim. distance between plates, I 

 obtained 1040*02 centim. 



The thickness of the ebonite; plate was measured by means 

 of a micrometer-screw specially constructed for the purpose, 

 and fixed in a brass frame. This brass frame was so large that 

 the screw could be brought to any point on the dielectric. 

 That portion of the ebonite plate which lay between the con- 

 denser-plates was divided up into squares, and the thickness 

 of the ebonite was measured at the corners of these squares. 

 The value given above is the mean of measurements taken at 

 twenty different places ; and Boltzmann f has shown that this 

 mathematical mean is to be taken, within the limits of error, 

 as the true thickness of the dielectric. 



The first of the ventral segments just found, 041*03 centim., 

 corresponds on the curve mentioned above to a separation of 

 the condenser-plates of 0*791 centim., wben air alone is be- 

 tween them. Therefore the capacity of tbe condenser, with 

 plates-0*7 ( Jl centim. apart and air only between them, Is the 

 same as that of the condenser with plates 1*200 centim. apart 

 and the ebonite disk between them. The difference, 0*475 

 centim., represents the increase of thickness of the condenser 

 in consequence of the insertion of the ebonite plate. 



For the position of the second ventral segment, 585*40 

 centim., we had in the air-condenser a thickness of 1*200 

 centim., and after Inserting the ebonite it became 1*701 centim. 

 The difference is 0*495 centim. 



Vov the third ventral segment, 1040*92 centim., we had in 

 air a thickness of 1*234 centim. The difference is, in this case, 

 0*467 centim. 



These three differences, 0*475, 0*495, and 0*407, should 



* Some of the original measurements are given in full in Wien. Ber. 

 xcix. pp. 483-480, 1890. 



f Boltzmann, Pogg. Ann. cli. p. 508, 1874. 



