112 



DISPLACEMENT INTERFEROMETRY APPLIED TO 



damp, semi-subterranean room, as in the former case, and the two instruments 

 were not very far apart. 



It was necessary to put the scale and telescope somewhat nearer (265 

 meters) to the mirror n, than before. The new instrument is thus apparently, 

 though not really, less sensitive than the other. As the scale-parts are given 

 in centimeters, the displacement of shot will be 



ii. 357(2X265) 



= ( 



cm. 



the needle being 22.7 cm. (between centers) long. 



89. Trial observations. Radiation effect. On testing the apparatus roughly 

 with a brass kilo, it was noticed that the first excursions were always abnor- 

 mally large. In the course of the day these died off to values scarcely one-tenth 

 of the original. An attracting ball of lead M, weighing M = 1,602 grams and 

 capable of approaching the shot to R = 5 cm., was then installed. Here again 

 the first triplet (14) obtained was enormous (19.2, 1.4, 10.6 scale-parts), but it 

 gradually diminished and on the next day the excursions were steadily of 

 normal value (about 3). It seemed probable, therefore, that an extremely 

 subtle radiation effect was here in action. To test this, the lead ball M was 

 removed and just exposed to a few passes of the Bunsen burner, so as to be 

 warm to the touch. On being replaced, the alternations (in approximately 



Q \ \_yr.. r_v \'_'.i 



\U /t>\ I\ A" A ;\ 



. k/8r\ /co\ /k_\ //vA A..\ /..\ 



600* 



half -hour periods) obtained (fig. 140 a, scale one-tenth of the preceding) were 

 enormous, the first excursion being up to the wall of the case. They gradually 

 decreased, as the figure shows, but the effect was still very great, the initial 

 triplets (within the first hour) being 22 and 1 8, or 6 or 7 times as large as the 

 normal gravitational effect and of the same sign throughout. The remarkable 

 feature of this is the long time needed for the effect to pass off; for, after more 

 than an hour, the ball M was again quite cold on the touch, but its radiation 

 activity was nevertheless still pronounced. 



The next day the same ball, whose natural excursion was but 2.5 (fig. 1406), 

 was merely warmed by the hand (fig. 140 c). The result is an excursion of 



