■1.) 



Tlie following are the results of tlie me.nsures upon tlie F line. 



Date 



X.. 



. of Obs. 



Value of h 





/ 



Dec. 4 





4 



4P 2(r 30 



.1 



4SG0.17 



• • •> 





3 



., V 29' 





„ .14 



1? i» 





3 





.3 



„ .15 



., 5 





3 



., ., 30- 



.1 



., .17 



'» «1 





3 



., ., 30' 



.3 



„ .17 



• 1 •» 





4 



., „ 29- 



.8 



„ .IG 







Mean o 



f 20 observations 











/. 



= 4S00.1(] 







G 



(Jwiiig to the inferiority of tlie spectrum on tlie west siile of the normal, 

 which has already been disciisseil, this line could not be seen there with sufficient 

 distinctness to make direct measurement desirable. Tlie oi instruct ion of the 

 instrument rendered it impossible to work npon it in the spectrum of the tirst 

 order, and, as it was but little more than 5° from F in the second order it was 

 tliought that the most accurate determination would be made by referring it to 

 that line which was accordingly done. It is recognized, of course, that errors 

 in gmting adjustment, which will intlnencc the results of this measurement by 

 an amiiunt proportional to the dilVtierice of the secnnts of the two angles, are of 

 greater importance here than in any other instance; but tlii.< dilVerence is still 

 small and the error must be greater than is supposed to have existed in any case 

 in onler to produce a sensible effect. Besides, this adjustment was made live or six 

 times during the meivsurement and tlie intluence of accidental errors must be 

 eliminated to a great extent. The uniformity of tlie results proves that such 

 errors must have been extremely small.— The following are the results. 



Date 



No 



. of Obs 







Value 



of/. 



/ 



Dec. ß 





6 







35= 54 



46 '.2 



4307.19 



7 





4 







r» M 



47". 4 



„ .23 



i> n 





4 







II II 



45".G 



I, .18 



II It 





3 







)l 11 



45".7 



„ .18 



»> » 





4 







II 11 



45".6 



., .18 







Mean 



of 



21 



observations 











/ : 



— 



4307.19 







