EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 17 



had little or no influence on the result. An interesting fact is the depression 

 produced by the gale on March i (see g in fig. 12). Though the behavior of the 

 apparatus, as such, apart from the anomalously large results, was throughout 

 satisfactory, it was supposed that the attack of water on the soldered joints 

 of the copper float was an objectionable feature. These were accordingly 

 covered with resinous cement, with a removal of this trouble after March 13, 

 the new zero being indicated at n in fig. 12; but the behavior thereafter was 

 even more variable than before, showing that something not connected with 

 the change of inclination is in question. 



10. Observations, continued. The horizontal pendulum was now read- 

 justed for greater sensitiveness and for a smaller vertical inclination <p, by 

 moving the upper pivot inward. Since T 2 varies as i/<p, considerable displace- 

 ment is required to change T markedly. The period found was T = 2 5 seconds, 

 all the other constants remaining unchanged. Hence, since the original period 

 corresponded to T =20 seconds, <p' = 0.014 radian, the inclination is now 



400 ,. 



^ = 0.0147 - =0.0090 radian, or 0.51 , nearly. 

 025 



Since a = <pd radians, and since d = x/$D, where D = goo cm., 



o.oooo 



a= - , - x radians = 0.5 15* second. 

 3,600 



Thus a centimeter of distance between the two slit images corresponds to 

 about 0.5 second of arc of inclination of the pendulum axis. 



" 



0" 



6 S 



FIG. 13. 



The damping was as before moderate, due only to the axial float. 



The new data given in fig. 13 in arbitrary units (to be reduced 5.74 times 

 to refer them to seconds of arc) show the same peculiarities as the preceding. 

 The range of variation is of the usual abnormally large value. There is no 



