VISCOSITY OF WATER BY THE EFFLUX METHOD. 105 
mined in the general case. Let P’, denote the pressure corrected 
for these frictional resistances etc. at the terminals, then since 
L, =L +1, we obtain from (2) 
wR*P, _«R* 8 yl 
8nq 8nq ah 
I, as we have said being either positive or negative. Combining 
this result with (3) and (4) and remembering that /, a function of 
R, denotes a small length of tube producing an equivalent loss of 
pressure to that arising from the friction at the ends, at the same 
time taking account of the positions of sectionsee’ and //,;’ and . 
therefore that it may legitimately be put under the form /=n &, 
the general formula for the evaluation of the viscosity may be 
expressed :— 
bE A Sa (12a) 
(Po - 
w R* 
y= Rathaus (P-—m 
in which n may have a positive or negative value, since 1 may be 
positive or negative. P'then in this formula, is the measured 
differences of pressure in the reservoirs, and Z the actual length 
of the tube. It remains to ascertain whether 2 has a constant 
value as supposed, and if so what the value is. 
(13) 
Pg” \ 
aw? R*’ 
Assuming that C has been found from J’, reduced by (3), or 
from 7’, reduced as indicated in (5), or preferably perhaps by 
extrapolation of a series of measures (11), we have at once from (13) 
crit C’ be used instead of C the numerator’ of the left hand 
member will be x gC’ R*. Ifnow the values of R/L be regarded 
48 abscissze and those of the first member of this equation as — 
ordinates, aline passing through the points so determined will 
‘ntersect the axis of ordinates at the distance 7 from the origin, 
‘and this line will make an angle with the axis of abscisse whose 
tangent divided by » is n, the required factor. The intercept on 
the axis of ordinates corresponds to the values R=0, or de a 
te, for the condition when the correction for resistances at the 
terminals of the tube is infinitely small in relation to the resistance 
