78 DR. JAMES BOTTOMLEY ON A 



Now compare B with C, whence, if and 0' be the lengths 

 of the columns, we shall have 



W R*^=W R r ^' (4) 



From equation (3) we have 



p-q 

 and from equation (4) we have 



q—r 



But these two values of R ought to be the same ; so we 

 ought to have the equation 



f-t ff-0 



p — q q—r 



The different tints I used consisted of BaS0 4 and lamp- 

 black. Tint A consisted of lampblack 0*012 gram, BaS0 4 

 10 grams; tint B contained twice the above quantity of 

 lampblack to the same quantity of BaS0 4 ; and tint C 

 contained four times the quantity of lampblack to the 

 same quantity of BaS0 4 . The absorbing-medium I used 

 consisted of water containing a minute quantity of lamp- 

 black in suspension. This, as I have before shown, behaves 

 nearly the same with regard to the absorption of light as 

 if the carbon were in solution. 



A comparison of tint A with tint B gave R = &' 3 . Tint 

 A compared with tint C gave H = k'* 46 . Tint B compared 

 with C gave R = &' 4 . Inasmuch as k is a fraction, these 

 three values of R will not differ much. The experimental 

 inquiry is difficult ; and the following defect is likely to 

 have some influence on the result. The grey powders were 



