of the Lengths of Waves of Light. 



491 



71-1 



That no appreciable errors can have thereby arisen in the 

 mean values thus obtained — values which may be regarded as 

 true for 15° C. and the mean barometric pressure — is readily 

 seen on calculating the magnitudes of these corrections. 



Assuming the refraction-coefficient of air to be 



71 = 1-000294, 

 to be a constant magnitude, independent of temperature 



and pressure, and the value of e, moreover, to hold for 15° C, w ; 

 obtain the following corrected value : — 



p sin (h) 



log A= log -0-36 {t °- 15°) + 0-09(4°- 15°) 



m -0-04(H-0 m -76), 



whence we conclude that the correction for log A, amounts to 



+ 0-45 (*°-15°)-0\L4 (H-0 m -76), 



expressed in units of the fifth decimal place. 



Accordingly a change of 2 degrees in temperature produces a 

 change of 2" in the value of the angle ©, if & be assumed equal 

 to 25°; this error is comparable with the error of adjustment 

 itself. For smaller values of® the error will of course be smaller. 



The angle ® is also subject to a correction dependent upon 

 the absolute motion of the instrument in the direction of the 

 path of the incident ray ; this correction, however, is almost in- 

 appreciable for the observations upon which the numerical values 

 in the following Table are founded. 



The wave-lengths are, like those of Fraunhofer, expressed in 

 units whose magnitude is equal to 0*00000001 of a Par. inch. 



Table I. — Wave-lengths, in 



100,000.000 



ths of a Paris inch. 



B. £ 



73 



a 



3 

 U 



u 



<u 



ft 



t/2 



3 

 2 



3 



C. 



a 



03 



a 

 go 



D. 



a 



3 

 S-i 



u 



03 



ft 



E. 



a 



a 



s- 



a 



o 



b. 



2 

 5 



o 

 02 



F. 



a 



a 



— 



o 



=~ 



G. 



a 

 | 



03 

 Oh 

 t/2 



H. 



a 



3 



a 



ft 

 5Q 



H x . 



£ 



a 



o 



2426-50 

 2426-28 

 2426-23 

 2426-33 

 2426-25 

 242627 



1 



2 

 2 

 3 



1 

 2 



2178-69 

 2178-53 

 2178-62 

 2178-64 

 2178-57 

 2178-61 

 2178-56 

 '2178-48 



3 

 3 

 2 

 I 

 4 

 4 

 2 

 4 



1948-25 

 1948-21 

 1948-24 

 1948-20 

 1948-25 

 1948-24 

 1948-23 

 1948-32 



3 

 2 

 1 

 3 

 3 

 3 

 4 



1916-51 

 1916-64 

 1916-46 

 191653 

 1916-56 

 1916-49 

 1916-43 

 1916-47 



1 



3 

 2 

 4 

 1 

 4 

 4 

 4 



1797-38 

 1797-37 

 1797-21 

 1797-27 

 179705 

 1797-20 

 1797-11 

 1797-55 



1 



3 

 3 

 2 

 1 

 3 

 2 

 4 



1592-32 

 1592-53 

 1592-22 

 159216 

 1592-50 

 1592-32 



2 

 1 

 2 

 2 

 2 

 2 



1467*19 

 1467-58 

 1467-32 

 1466-66 

 146712 

 146734 

 1466-98 



1 



4 

 3 

 2 



4 

 3 



1454-88 

 1453-39 

 145374 

 1453-89 



4 

 3 



2 

 1 





2426-29 





2178-59 



1948-24 



1916-50 





1797 27 1592-34 





1467'18 





1453-98 





2K2 



