68 EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 



The observations were made in time series, when the plates were close 

 together. For plates farther apart this is not essential, but in the absence 

 of other than the air-damping the suspended plate oscillates, so that mean 

 values have to be taken. It will be necessary to await the summer in order 

 that all observations may be made in a room free from artificial heat. 



In table 7 and fig. 41 A I have inscribed the first observations from plates 

 close together. In table 8, the summary of all the observations is given. In 

 series i to 4, table 7, the plates are probably not far enough apart, though 

 the contact position is still beyond the equilibrium position by about 0.014 

 cm. It was not necessary to wait for the uncharged position of the plates, as 

 this remained pretty constant long before and after the experiments. In 

 series 5, 6, 7, and 8, the distance apart is increased about 0.042 cm., and there 

 is no danger of actual contact (free space 0.056 cm. when charged), so that 

 actual repulsion is in question. 



TABLE 8. Summary. 



Table 8 shows the essential data of these and subsequent experiments in 

 which the distance d, in centimeters, between the plates is gradually increased. 

 A7V shows the difference of displacement (in centimeters) observed, when plates 

 were respectively charged and uncharged. A A/" thus measures the displace- 

 ment of the suspended plate in half centimeters. From A7V the approximate 

 electric force (ignoring the repulsion of plates) may be computed as above, 

 F' R = 6$.2&N. This is given under F' R computed, in the seventh column. 



Plates were charged by aid of a storage battery to the potential shown under 

 V bs (volts), in column 4. From V and d, the attraction of plates F' R may be 

 computed, since 



A = wR- being the area of each plate. The results are given in column 6 

 and the ratio F/F' in column 9. 



Furthermore, the potential V may also be computed from F R , since 



d 



and this is inserted in the fifth column. 



