110 



DISPLACEMENT INTERFEROMETRY APPLIED TO 



room, of practically constant temperature. In any given series, for instance, 

 the behavior is consistent. The repulsive force retains its relations relative 

 to the gravitational attraction, changes sign with it in a consistently different 

 phase, in each of the series of results. If there were any approach to reso- 

 nance between the period of the alternating force and the needle, an explana- 

 tion of the results might be attempted ; but the semi-period of the needle may 

 be estimated at 10 or 20 minutes. It is aperiodic, practically creeping. 



87. Further observations. The needle was now dismounted and the obser- 

 vations of 84 on the elastic coefficient of the needle were concluded. After 

 it had been put together again with improvements, and readjusted, the 

 observations of figures 133, 134, 135, one and two minute periods, were then 

 taken. The observer throughout kept at a distance from the apparatus except 

 at the time of reading the telescope. It will be seen that the observations for 

 one-minute periods again fail in the usual way. For the three-minute periods 

 the results are normal, as the needle swings with apparent inertia after turning 



o itr ar 

 U i 



I** y/l" 9/T*- 



1(T SO" 



0* 1 



the attracting weight M. The observations (fig. 135) for two-minute periods are 

 also normal in this respect; but it is necessary to reckon from observations 

 midway between the turning-points if triplets are to be available. The data are : 



Series 21 * = 3 m Ay =1.30 io 3 A% = i8.p 10*7 = 4.4 

 23 2 m .61 8.9 4.6 



about of the same order as above. The displacements A* are again roughly 

 in the ratio of 9 14. But the new results are no improvement on the old. 



As a final condition of safety the hooks of the quartz fiber were additionally 

 secured with sealing-wax to the torsion-head above and the needle below, so 

 that the system throughout was free from any loose parts or movable joints. 

 Results so obtained for three-minute and one-minute periods are given in fig- 

 ures 136 and 137. The latter again completely fail. The former are not essen- 

 tially different or better than the above. The fiber was a little shortened by 

 accident. The value of the successive triplets is given on the curve. Their 

 mean value is 



Series 24 * = 3 m A>>=i.i7cm. io 3 Ax = i.7 cm. 

 What is particularly noticeable in figure 136 is the uniform motion within the 

 branches of the zigzag. 



From the data as a whole we may conclude that, in addition to gravitation, 

 some other force is present, attractive or repulsive, and in any given experiment 



