174 Ernst Lecher on the Measurement of 



rough preliminary experiments the approximate relation be- 

 tween the position of the ventral segment and the distance 

 apart of the plates was found, and then the position of the 

 ventral Begment was determined as accurately as possible for 

 one or two of tlir distances found above. Thus, finally, in the 

 two eases which I compared together, the fundamental oscil- 

 lation was tlu v same; the slider was in exactly the same 

 position, only the distance apart of the condenser-plates at the 

 ends of the wires was different, according as air or tho sub- 

 stance experimented upon happened to be between them. 

 Since in the two cases everything remained absolutely the 

 same down to the capacities at the ends, I inferred that these 

 capacities were also equal to each other, and thus the dielectric 

 constant of the substance under examination (or rather the 

 quantity to which this name is often erroneously given) could 

 be determined in a simple manner. 



If the space botween the condonsor-platos was filled with 

 air wo had, corresponding to distances apart of tho plates, 



0-791, 0-830, 0-870, .... 1-146, 1-186, 1*227, 1-266, 

 1-324, 1-360 centim., 



the following numbers as the mean distances of the ventral 

 segment a from the end 5 of the wire, 



641-48, 633-68, (529-18, .... 592-74, 586-72, 583-84, 

 580-35, 573-65, 570*54 centim. ; 



and further, corresponding to an air-condenser with plates, 



1-146, 1-186, 1-227, 1-266 centim. 



apart, the mean distances of the ventral segment c from the 

 cud ,s- of the wire were respectively 



1045-74, 1043-70, 1041-73, 1038-64 centim. 



The meaning oi' a and is the same as in the paper on 

 electric resonance previously referred to. The wave-lengths in 

 the two cases are in tho proportion of 1 to 2. For each 

 distance apart of the condenser-plates, ten adjustments of the 

 slider were made. After every measurement the slider was 

 displaced by an assistant to such a distance that the vacuum- 

 tube became quite dark, so that each new adjustment was 

 found by drawing the slider along the wires with extremely 

 great care. In spite of this, the greatest deviations amounted 

 to 5-6 centim., but usually they were smaller than this. In 



