424 



PROCEEDINGS OF THE AMERICAN ACADEMY 



TABLE II. 



set, the ordinates of the straight line were obtained, to these were 

 added the ordinates of the residual curve for the same times after sun- 

 set, both readings being in logarithms of the original observations ; 

 this logarithmic sum was now doubled, the sign changed, and the 

 figures so obtained were used as ordinates for a new curve, the ab- 

 scissas being the times. From this last curve we obtain directly the 

 logarithm of the number which would represent the proportion of 

 light at any minute as compared with that at sunset, which we call 

 unity. 



