68 



Mi 



Let a (Fig. 1) be an end face of a rectangular parallelopiped suspended from 

 one arm of a balance, with its lower face horizontal, and therefore parallel to the 

 liquid surface OA''. Call w' the weight of the frame (block) in this position. 

 Lower the frame until it touches the liquid, and bring it again to the first position, 

 as in /;. The weight of the frame is now increased bv the weight of the liquid 

 raised above the level surface. As the frame is raised, the weight increases for a 

 time then suddenly decreases, passing through a distinct maximum. Call ?/^ the 

 total maximum weight. The net maximum weight is 



\o = w" — w' ^ 2 Z' sin a + ply, ( 1) 



where T^the surface tension in grams per centimeter; 



a = the angle between the A'-axis and the tangent to the liquid surface at 

 the edge of the frame ; 



i =^ the thickness of the frame ; 



p = the density of the liquid ; 



y r=z the height of the frame above the li(iuid surface ; 



/ =r the length of the frame, one centimeter. 



Also, 



fo ^ 



//'/.'■, 



dx T cos n 



(2) 



dn 



i>y 



Placing c^ 



— , and remembering that , 



/) ' '^ d. 



ciy 



da 



dy 



tan «, 



y^ = — 2 c^ cos 'i -\- k. 

 When )/ =^ o, « = o, and A- = 2 c^. 



y 



2c 



1 — cos a 



= 2 ^ sin 



2 



