with the Aid of, a Grating. 



425 



The values of equation (11) for successive Fraunhofer 

 lines and for a = 3° have been computed in Table II. for the 



Table II. 



Path Difference, — 2{y m — i/ n ) cos ot + eZ l — eZ 2 -\-eZ 3 . Light 

 crown glass ex. = 3° throughout. Grating si 

 •000351cm. 1 = 45°. e=l cm. 



?pace 



Spectrum lines... 



= 



B. 



D. 



E. 



F. 



G. 







\xio s = 



68-7 



58 93 



52-70 



48-61 



43 08 



cm. 





ix = 



1-5118 



1-5153 



1-5186 



1-5214 



1-5267 







R = 



27° 53' 



27° 49' 



27° 45' 



27° 42' 



27° 35' 







r = 



29° 26' 



29° 22' 



29° 18' 



29° 14' 



29° 8' 







Pi = 



26° 16' 



26° 12' 



26° 8' 



26° 5' 



26° 0' 







a = 



3°0' 



3°0' 



3°0' 



3°0' 



3°0' 







;--R = 



1°33' 



1° 33' 



1° 33' 



l°-33' 



l c 33' 







r-fa = 



3° 10' 



3° 10' 



3° 10' 



3° 9' 



3° 8' 







Zx = 



3-4160 



3-4218 



34272 



3-4318 



3-4403 



cm. 





z 2 - 



656 



714 



767 



808 



'896' 



cm. 





z 3 = 



689 



747 



799 



841 



928 



cm. 



Path Difference, 

 « = 3°; 



H 



-1-9992. 



- 1-9992 



-1-9992 



-1-9992 



-1-9992 





e = \ cm. ; 

 y— 1 cm. 



4-3-4193 



-|- 3-4252 



+3-4304 



+34352 



+3-4436 





The data are merely intended to elucidate the equations. The values Z 

 are nearly equal. So also the cases for a— 3° and a = 0°. 



siime glass treated in Table L, the data being similar and in 

 fact of about the same order of value. The feature of this 

 Table is the occurrence of nearly constant values, a = i— I, 

 r — R, and r.-r&u throughout the visible spectrum. Hence 

 if the following abbreviations be used : 



A=cos« = -9986, B = cos (r-R) = '9996, 



C = 1 + cos (r - Bi) = 1*9,984, ' 



A, B, C are practically functions of a only and do not vary 

 with colour or \. Furthermore, if the path difference is 

 annulled at the E line, equation (11) reduces to 



n\—2eA(fjb/coB'R—/jL cos R E ) + g{C— 2AB)ft/cos r, 



where 2eA and e(C — 2AB) are nearly independent of X and 

 Phil. Mag. S. 6. Vol. 21. No. 124. April 1911. 2 F 



