ON THI-: APPLICATION OF INTERFERENCE METHODS 



t'ipal section of the polarizer and the axis of the first quartz, and (o the an<;le 

 between the axis and the analyzer, the intensity of the light transmitted 

 will be 



I=ros' ((0—7.) -.s7/( 2 rj. siii 1 o) .s//r - — ^-^ -i 



^ /. 



where /, is the thickness throu":!! the fii-st (juartz. and i-, that thiough the 

 second. If the analyzer and jwlarizer are iiarallel, 



0): 



whence 

 and 



.01, and /=l_.s<V2 7..svV7:^^^^, 

 /,=1, aud J.. = l-sin- 2a, 



V= 



/, — /o _l —cos^ 2 g 



/i + /o~l + C0S'2 7.' 



This cm-ve, together ^ath the mean of a number of eye-estimates, is given 

 in Fig. 2, Plate I. From these the following table of con-ections may be 

 obtained : 



u.oo 



.05 

 .10 

 .15 

 .20 



.30 

 .35 



.411 

 .45 



.51) 



Cor. 

 0.00 

 + .03 

 + .04 

 + .03 

 -r.02 



.00 



-.03 



-.05 



-.07 



-.08 



.10 



K. Cor. 



0.55 -0.12 



.60. 

 .65. 

 .70 

 .75 

 .80 

 .85. 

 .90 

 .95 

 1.00 



-.14 

 -.15 

 -.16 

 -.16 

 -.14 

 -.13 



.11 

 -.08 



.00 



Tlic curves .show a general tendency to estimate the visi])ility too high 

 when the interference bands are cleai'. and too low when they are indistinct. 

 This tendency may be modified by a number of circumstances ; — thus, it in- 

 crea.ses witli the refi-angibility of the hght used ; it is greater when the field 

 contains a large number of bands lliaii wlicn there are but few ; it is gi-eater 

 while the visibility cur\'e is falling than when it is ri.'^ing; it does not seem 

 to be greatly affectted by the inten.sity of the light ; finally, it varies on dif- 

 ferent occasions and witli (litfcrcut obson'ers. Notwitlistanding these dis- 



