ie 
: 
VISCOSITY OF WATER BY THE EFFLUX METHOD. 117 
numerator it may be put in the denominator in the form 1—¢. The 
general ‘mean radius of efflux’ R is of course determined by the 
equation 
2G) ten 
15. Flow in a tube whose sections are ovals of unequal area and 
uncertain contour.—Owing to its actual irregularities of form 
perhaps the theoretically least exceptionable method of determin- 
ing the volume of a capillary tube and its mean radius of efflux, 
is to measure the former directly and compute the latter from 
measurements of the greatest and least diameters of its sections. 
The volume furnishes at once the radius of an equal right circular 
cylinder, and this radius may then be corrected so as to give the 
‘mean radius of efflux,’ the corrections involving terms depending 
only upon the excentricities of the sections, and being therefore 
small. 
If in formula (25a) § 13 we put! 
we may write “ is 
Bin Bn = Rn (1 ~ p?)3 cdl 
If now the excentricity of the terminal sections be nearly the 
Same, or since we do not assume that the sections are ellipses if 
bo Seema of the minor to the major axes be nearly equal for both 
Th = L(+ &) 
* Square of the radius R, of a right circular cylinder of equal 
Volume will then be 
2 
V ; 2 
P= > = Ra (l +5) (1—e*) 
With sufficient precision. This last equation enables us to replace 
er &.,, that is by the radius determined from actual measure- 
t of the Capacity of the tube. After some reduction and 
snag RTD NE Ne certs 
: Bn in this formula has of course the same value as in (26) in the 
Section and p=4(b+c). is 
