16 EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 



the constant T only had to be changed, the former value of <p being <p' = 0.014 

 radian and T=2o seconds. Hence, 



/ 400 ,. 



<f> = <P 7-7 ^ =0.0214 radian, 



(l6.2) 2 



or about 1.2 degrees, roughly. This is an unnecessarily large angle and is 

 merely admitted as a first experiment, to be decreased in successive experi- 

 ments. Hence, finally, 



a = >0 = 6.oXio- 6 # radians = 1.23* seconds of arc. 



The apparatus is thus relatively insensitive, seeing that 1.2 seconds go to a 

 centimeter of deflection, x. 



200 

 480 



16Q 



440 



/20 



100 



60 



60 



40 



20 







-20 

 -40 

 -60 

 -80 



A 



4 



n 



25 



5 7 9 // 

 FIG. 12. 



15 17 



60 l 



4(f 



30* 



10" 



JO" 



0" 



These observations were carried on for some time in the midst of other 

 work, during February and March of 1914, the method of reflection being used. 

 The data are first given in fig. 1 2 . The ordinates of the latter are in arbitrary 

 units and must be divided by 5.74 to reduce them to seconds of arc. In the 

 continuous record from February 23 to March 13, the range of variation is 

 almost as large as it was in fig. 9, showing that the use of jeweled bearings has 



