VISCOSITY OF WATER BY THE EFFLUX METHOD. 115 
doubtless frequently sensible: it has already been pointed out— 
§ 11—that in those used by Poiseuille only one instance occurred 
of uniform diameter. We proceed therefore to consider the flow 
in a frustum of right elliptical cone. 
The general considerations are identical with those of the pre- 
ceding article. To determine the velocity for any section we 
substitute in (22) BC/(B, C, ) for R? /R;: hence taking account 
of the law of velocity expressed by (20), or otherwise directly from 
(18), we have 
= A ae i eee () 
The ratio of B and C will be the same for every section, let 
therefore 
8 = }(B+C) ande = ane 
(g) then becomes 
dp 8y 1+é 
dz as * (1-<)? 
R being the only variable in the right hand member. The 
| solution of this is identical with (23), hence we write at once 
a ee Bi Ln Bin tanks +8n) 1+e (25) 
q SBnBe (1 -€*) ete 
q The value of the ¢ term is 
144249 <4 anc 
me ae ea 7 a 
This last equation may be expressed similarly to (23) since 
~~ m+ BmBn+ Bn) (1-€?) 
thus 
Pets: . Vo, qs ‘ (25a) 
e.. Base —é€*) 
The expansion of the final ak is 
iE — 5 2 } 4 ie Se hie me 
_ e* + l4e* + {be + lie 
volume V,, may be found by filling the tube say with mercury. 
Practical application of the formula is obvious. 
