178 



Ernst Lecher on the Measurement of 



Water.— If I poured into the wooden ring distilled water 

 (the thickness of the water alone being 1*9342 centim.), I 

 found, with condenser-plates 3*160 centim. apart, a ventral 

 segment a at 635*47 centim. 



The difference calculated as in the case of petroleum gives 

 in this case 1*953 centim. for a thickness 1*934 centim. of the 

 dielectric. The error of experiment is therefore now too 

 great, and if I wished to calculate the dielectric constant 

 from these data as before, its value would be infinite. 



Experiments with Ruhmkorf Oscillations. 



In the determination of the dielectric constant by means of 

 EuhmkorfF oscillations, I have adopted a method which is 

 very convenient and simple and permits very exact measure- 

 ments to be made. This method is in many respects similar 

 to that used by Gordon *, but is much simpler. One pole of 

 a small induction apparatus li (fig. 2) is put to earth; from 

 the second pole one connexion is made to the condenser C 

 and a second one to the comparison condenser E. The other 

 two plates of these condensers, C and E', are connected to 

 the two quadrants q and q' of an 

 electrometer by means of two 

 parallel wires. The needle I of 

 the electrometer is put to earth. 

 The action of this arrangement is 

 immediately seen. If the two con- 

 densers are equal, both quadrants 

 are alternately charged and dis- 

 charged in the same manner, and 

 the needle remains at rest. If the 

 one condenser is stronger, the elec- 

 trometer-needle is momentarily 

 deflected towards the correspond- 

 ing quadrant. 



The plate to be experimented on, 



ecLTth 



ctrblt, 



xx' , was then placed between the 



disks of the condenser CC, and the 



other one EE' (an ordinary Kohl- 



rausch plate-condenser) was roughly adjusted. The final 



adjustment was made by the micrometer-screw of the con- 



* G. Wiedemann, Elektricitat, ii. p. 38, 1883. After this paper had 

 been communicated to the Vienna Academy (16th May, 1890), the con- 

 temporary work of Donle was published (Wied. Ann. xl p. 307, 1890). 

 Our methods are almost identical, except that I use in place of an electro- 

 dynamometer an electrometer, which I consider in several respects more 

 simple and advantageous. 



