518 



Mr. A. Ferguson on the Theoretical 



equation (x.). With drops large or small, provided they 

 exhibit a maximum point at which a vertical tangent may 

 be drawn, little difficulty is experienced in hitting off the 

 precise coordinates of the point at which the tangent is 

 vertical. Measurements involving the use of equations (xi.) 

 and (xii.) are quite straightforward, and an example of the 

 use of (x.) will serve to exhibit the minimum trustworthiness 

 of the method. 



All measurements were made by an "x-y" microscope, 

 as described above, the vertex of the drop being taken as 

 origin. 



Details. 



Fluid : tap-water. 



Temp. 11° C. 





Table I. 





X 



y 



xy 



X 2 



3-606 



1-7155 



6-187 



13-00 



3-515 



1-6135 



5672 



12-36 



3-115 



1-2235 



3-814 



9-703 



2-715 



•9055 



2-458 



7-371 



2-315 



•6515 



1-508 



5-359 



1-915 



•4285 



•8209 



3-667 



1-515 



•2705 



•4099 



2-295 



1-115 



•1435 



•1600 



1-243 



•715 



•0605 



•0433 



•5112 



•315 



•0135 



•0043 



•0992 



With similar figures for 

 negative values of x. 



Magnification of drop on photo = 16*07. 

 At the point for which ^> = 45°, 



^ = 3*502, ^ = 1-600. 



Hence, true values of x± and y± are given by 



jg^-.lbU, #i- i 6 .07 



0C\ — 



yi =™ =-09959. 



A curve between x and y was plotted on squared paper, 

 and its area between the proper limits as fixed by the points 

 (o&i, t/i) and ( — # l5 y x ) was measured by the planimeter and 

 was found to be 381 sq. cm. 



Also 1 sq. cm. on paper = '02 sq. cm. on photo. 



Hence, 



381x^02 

 true value of A (vide equation (x.)) = nr . iyjzj ='02952. 



