OF TOTAL DAYLIGHT DURING A SOLAR ECLIPSE. 203 



about 7 ; and frequently the sun was obscured by heavy 

 cloud, though at intervals it shone clear and bright. 



By arranging the 42 different observations of the in- 

 tensity of daylight into 9 groups, we eliminate the varia- 

 tions among the separate consecutive observations arising 

 from the unfortunately variable state of the weather, and 

 obtain the following series of regularly diminishing and 

 increasing numbers, giving the chemical intensity (I) of 

 total daylight occurring during the eclipse for the apparent 

 solar times indicated : — 



Time. 



I. 



Time. 



I. 



7*^57"" ••.. 



.. 0-590 



9** d^ .... 



.. 0-005 



8 8 ..., 



,.. 0-320 



9 15 • • 



... 0.102 



8 16 .... 



.. 0-270 



9 ^5 •.- 



... 0-140 



8 28 .... 



O'lIO 



9 31 ... 



,.. 0-125 



8 45 .... 



,.. 0-090 







In order to determine how far these values of chemical 

 intensity correspond to the numbers giving the relative 

 areas of the solar disk remaining uneclipsed, it is neces- 

 sary in the first place to allow for the variation in chemical 

 intensity caused by alteration in the sun^s altitude from 

 the time of first contact at 7^ 44"^ 6^ until the point of 

 last contact at 10^ 21°^ 7^. On a former occasion (Phil. 

 Trans. 1867, p. 559) I have shown that the relation be- 

 tween the sun's altitude and the chemical intensity is 

 represented by the equation 



CI,=CI„H- Const, xa. 



Where CI„ signifies the chemical intensity at any altitude 

 {a) in circular measure, CI„ the chemical intensity at the 

 altitude 0°, and Const, is a number to be calculated from 

 the observations. In default of any special series of ex- 

 periments made at Jamkhandi for the purpose of ascer- 

 taining the value of the constant at that place, I take 

 the determinations made at Para {loc. cit.) (in lat. 1° 25' 

 S.) as probably giving a fair approximation to the truth ; 



