DR. JAMES BOTTOMLEY ON COLORIMETRY. 177 



Case II. Let y{r = (f}cr, where ^ is a scalar. 

 Then 



and 



^Sy;/<l>a- . dv+^Sy;/a . <j>dv=^(f)Sayds. . . . (VIII.) 



Stokes's theorem can be made by similar treatment to 

 give varied forms^ both more and less simple. 



XXI. Colorimetry . — Part IV. 

 By James Bottomley, D.Sc. 



Read before the Physical and Mathematical Section, April 13th, 1880. 



On the Colour -relations of Nickel and Cobalt. 



For some experiments which I was making in colorimetry 

 I wished to obtain a solution which would absorb all the 

 kinds of light in the same ratio^ so that whatever sort of 

 light we started with, after penetration through such a 

 solution, it would remain the same in character, the only 

 variation being a change in intensity. Hence through 

 such solutions white surfaces would appear grey of various 

 shades, verging towards blackness as the length of the 

 column increased. Such a fluid we might call a soluble 

 black. I am not aware of any single fluid that fulfils the 

 above conditions. It might be said, Why not use ink ? but 

 such specimens of ink as I have examined are bluish or 

 violet on copious dilution. Moreover the colour alters 



SEH. III. VOL. VII. N 



