﻿Measurements of Pendent Drops. 4:2; 



The value of the constant b in the equation y — bx 1 h 

 obtained from the ordinary condition 



S(i/ — bx 2 ) 2 = minimum, 



the condition for which, viz. : 



92 



gives at once 



b =22(2/-^ 2 )(-^)=0 



-^ = -wu ~ . 1174- 



2a? 4 ~ 20-702 



Using the values of x in the fourth column and the equa- 

 tion «/ 7 — '1174 a? 2 , the eighth column was computed. The 

 ninth column shows the difference between the observed and 

 calculated values of ?/, the difference in nearly every case 

 falling within the limits of experimental error, as the verniers 

 used read to '001 cm. 



In deducing a value for the surface-tension from these 

 measurements, it is to be remembered that all lengths Lave 

 to be divided by the magnification to obtain their true values ; 

 b, whose dimensions are those of the reciprocal of a length, 

 must be multiplied by the magnification ; whilst by, which is 

 of zero dimensions in length, requires no alteration. 



At the vertex of the drop, the radius of curvature is given 



a-i- 1 



1/2 



and, therefore, in the equation 



2T 



/>' 



R 



gph 



we have T given In 



&> 



2 ~ 'lb ' 



In every case, however, in which calculations were made 

 using this formula, the values found for T were uniformly loo 

 low (about 70 dyne-cm. -1 ). It is probable that this is due 

 to the fact that the terms of inportance in determining the 

 value or are rather too remote from the vertex ; to remove 

 this difficulty, it will be necessary to use a higher magnifica- 

 tion,m order to measure y-coordinates still nearer the vertex 

 with a sufficiently high percentage accuracy. 



But, using the figures given above, a sufficiently accurate 

 estimate may be made by calculating the principal radii of 



