EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 53 



in their downward slope toward the left would be compatible with gravita- 

 tion. Release should take place at the intersection of the two lines. Results 

 of the same kind are shown in fig. 3iB, where the apparent repulsion is very 

 definite. It is probable that in both cases the discrepancies observed are dis- 

 torted by capillary forces, surface viscosity at the water damper, and by the 

 inclination difficulties. This is borne out by fig. 31 C, in which the fixed disks 

 were alternately placed all but in contact with the suspended disk. The curve 

 should have been zigzag, with the oscillations equal and in opposite directions ; 

 but it is quite irregular, due to extraneous causes. R and L indicate whether 

 the fixed disk is on the right or left side of the suspended disk. 



A A B 





\ 



cos 



coo 



005 



- -/ / -3 



FIG. 32. 



The water damper was now removed and the work repeated, relying on 

 the air-damping at the disks only. No difficulty was experienced in obtaining 

 the interferences ; but the results fig. 3 2 A show no evidence whatever of attrac- 

 tion. Similarly in the alternations of fig. 326, the curve which should have 

 been zigzag shows no regularity. Here again foreign disturbances have 

 masked the effect sought, although the displacements themselves were ap- 

 parently definite and satisfactory. It is therefore necessary to replace the 

 disks by a larger set, as is done in the next section. 



30. Observations. Plates of larger area. The brass plates were now re- 

 placed by a set larger in area but thinner, this being in the direction of the 

 improvement of method indicated. The same unnecessarily heavy steel 

 pendulum had, however, to be used, so that M= 1,250 grams, h = So cm., 

 ^=111.3 cm., <f> = 0.0108 1 radian, F R = ^2.g AN. The new brass plates were 

 identical in size, the mass being w = 46 8 grams each, the diameter 2^ = 20.3 cm., 

 and the thickness 0.17 cm. In place of gravitational attraction an apparent 

 repulsion, equivalent on the average to 0.0338 cm., or about 68 drum-parts, 

 was observed. 



The observations are given in table i and in figs. 33A, 336, 330, the arrows 

 showing the direction of successive observations. The abscissas denote the 

 positions Ax of the attracting "fixed " plate on the micrometer, the ordinates 

 the corresponding value of the displacement AN of the plate suspended from 



