Retardations, and on the Theory of Foucault's Test. 173 



Table II. 

 K 0^ = O, k6% 2 = 500. 



0/0. 



'• 



m 



i. 



<p/0, 



I. 



56-28 



0/0. 



I. 



o-ooo 



9-87 



0-980 



31-13 



1-001 



1-05 



1376 



0250 



10-13 



0-990 



35-78 



1-002 



52-89 



110 



924 



0500 



11-08 



0-992 



39-98 



1-004 



4409 



1-20 



576 



0-800 



14-71 



0-994 



46-81 



1-006 



3527 



1-50 



2-59 



0'900 



18-51 



0-996 



5413 



1-008 



29-03 



2-00 



1-21 



0-950 



23-27 



0-998 



58-81 



1-010 



2614 



00 











0-999 



59-36 



1020 



20-89 











1000 



- 



58-50 











Table III. 





fcdi;i = 7r, 



*<9£ 2 = 500. 





0/0. 



i. 



0/0. 



I. 



o-oo 



0-32 



101 



8-98 



0-50 



0-48 



1-02 



6-57 



91 



2-46 



1-23 



0-58 



0-98 



7-55 



1-55 



013 



0-99 



9-90 



1-86 



0-05 



100 



2551 



00 



o-oo 



In the practical use o£ Foucault's method the general 

 field would be darkened much more than has been supposed 

 above where half the whole light passes. We may suppose 

 that the screening just cuts off the central band, as well as all 

 on one side of it, so that 0^ = ^. In this case (7) becomes 



sinT[Si(^ + ^)?+Si(^--^)f-Si(l + ^)7r-Si(l-^j9r] 



+ cosT[Ci(<9-<£)f-Ci(0 + <£)f + Ci(l + 0/0)ir 



-Ci(l-<£/0)7r]. . . (28) 



We will apply it to the case already considered, where 

 0f = 500, as before omitting Oi(0 + $)[; and equating Si(0 + <£)f 

 to \ir. Thus 



I=[i7r+Si500(l-^)-Si(l + ^>/6>)7r-Si(l-(^/6>)7r] 2 

 ^[CiSOOCl-^ + CiCl + ^Tr-CiCl-cf)/^] 2 . (29) 



