ACOUSTICS AND GRAVITATION. 109 



two and three minute periods, the results in figures 125 and 127 become very 

 definite, as shown in the zigzags of the curves. The mean results would be 



Series 4 * = 3 m Aj=i.2Q io 3 Ax= 18.77 io 8 7 = 4-4 



6 2 m 0.30 4.36 2.4 



The former series (4) is still consistent with the preceding, showing that 

 Ax increased as P. The graph, moreover, is such as we should expect, the 

 needle being carried by its inertia after the turning-time of the force. In figure 

 127, however, the inertia retardations are just as large and the effect of this is 

 to depress the double amplitude and therewith the 7 value to one-half that in 

 series 2. It is probable, therefore, that the inaction during the first minute, 

 present to the same degree in series 3 to 6, or figures 124 to 127, needs some 

 other explanation, being referable to some peculiar repulsion, the nature of 

 which is to be ascertained. It is interesting to note in passing that if in figure 

 125 the displacement between maximum elongations had been taken, the mean 

 value would beA^ = 2.o, so that 7 = io~ 8 X6.S would be the result. This, 

 however, is merely accidental. 



On July 8 five series of experiments were made. The one-minute periods 

 failed, but the motion during the two-minute periods, one of which is shown in 

 the chart, figure 128, proceeded without apparent inertia. In series n. (two- 

 minute periods) the drift was excessive. The results were 



Series 8 t = 2 m Ay = 0.58 io 3 A* = 8.4 io 8 7 = 4-4 



9 2 .53 7.7 4-0 



10 2 .55 7.9 4-2 



11 2 .53 7.7 4-0 



The experiments made on July 9 and io finally exhibit a new state of affairs, 

 for here the needle is frequently in the same phase with the alternating force, 

 so that the motion of the needle changes sign midway between the turning - 

 times of the weight. I give two examples of these curious results in figures 129 

 and 130. In the former the general drift is very large and downward; in the 

 latter about as large, but upward. The value of the triplets is shown in the 

 indentations as before. The results were 



Series 15 * = 3 m Ay = 0.96 io 3 A# = i4 io 8 7 = 3 



17 , 3 1.81 26 6 



19 3 -57 8 2 



20 3 0.72 ii 2 



In figures 129 and 130 the oscillating motion of the needle is quite without 

 apparent inertia and the turning-points of the needle are such as to indicate 

 some periodic repelling force counteracting the gravitational attraction. In 

 order to get any data from these curves, the double amplitude of the needle 

 must be taken between the elongations, though their meaning then becomes 

 obscure. As compared with these figures, the phase conditions in figures 131 

 and 132 are again totally changed; for here the unknown repulsions operate 

 appreciably just before the attracting weight is turned. 



It is astonishing that results such as these should be obtainable with a 

 simple, carefully constructed apparatus, in a dark, damp, half subterranean 



