1870.] 



Observations in India. 



227 



both at Dehra, we carefully compared the two actinometers A and B 

 together. This was the only occasion during all our observations when 

 light clouds occasionally passed over the sun. But as the two instruments 

 were set up within 3 or 4 feet of one another, and as we both used the 

 same chronometer and read our scales at the same instant of time, there 

 appears no reason why the results should not be accurate, relatively 

 speaking. 



(7) The constants thus determined are as follows : — 



(Factor No. 1, to convert readings j 

 with glass on into readings 1=109 

 glass off. J 



B Factor No. 2, „ „ =104 



'Obtained from six groups 

 glass off and five groups 

 glass on , comprising sixty- 

 five observations in all. 



( Obtained from two sets of 

 | observations, each con- 

 J sisting of four groups 

 j glass off and three glass on, 

 j and comprising ninety- 

 \ six observations in all. 



Factor No. 3, obtained from comparisons between A and B comprising 



112 simultaneous observations, of which the following is a result-abstract 



reduced to 32° Fahr. and expressed in tenths of A's scale (both glasses on): — 





A. 



B. 





Apparent 

 time. 



A. 



B. 





Apparent 

 time. 



Observed 

 by 



J.H.N.H. 



Observed 



by 

 W. H. C. 



B-A. 



Observed 



by 

 W. H. C. 



bserved 



by 

 J.H.N.H. 



B-A. 



h m s 

 ii 26 

 080 

 51 

 2 11 



819 



828 

 758 

 786 



832 

 830 

 781 

 794 



13 

 2 



23 

 8 



h m s 

 11 44 



25 



1 51 30 



2 31 



788 

 804 



794 

 666 



806 

 817 

 816 

 681 



18 



13 

 22 



15 



Mean . . . 



798 



809 



12 



Mean ... 



763 



780 



17 



-, 7 , mean A 780 # 5 A . noo 



Whence -== A , =(r982. 



mean B 794*5 



We may also deduce 



(W. H. C. at B) — (J. H. N. H. at A)=ll. 



(J. H. N. H. at B)-(W. H. C. at A)=17. 



The accordance of these two average differences shows that no sensible 

 "personal equation" appeared to exist between the observers. 



(8) The observations simultaneous at Mussoorie and Dehra were, in 

 the first instance, separated into groups, and combined group by group 

 for a result. Subsequently groups were formed so as to include all the 

 observations taken, subject to the following conditions : — 



Seven (or fewer) sun-observations, with the intermediate observation in 

 shade, were combined to produce one result. 



Eight sun-observations, with the intermediate observations in shade, gave 



