124 G. H. KNIBBS. 
believe them to have the greatest weight. The corrections to the : 
pressures in these instances have been applied on the ann 4 
that m in formula (3) is 1°12. a 
There are thirty-six tubes in the series, the flow in the last four q 
is probably unsteady, and therefore the formula of reduction is of 
doubtful application, as it applies only to the case of steady motion. : 
The general result is F 
9 = 0013107 
and seems to be reliable to four significant figures. 
20. Values of the viscosity and relative fluidities between 0 and 
45° C. as deduced from Poiseuille’s experiments.—Interpolatioms. - 
—Poiseuille’s measurements with tubes A, C, D, and Z, give, to q 
quarter seconds, the times of efflux, for a volume constant for each — 
tube—excepting in so far as it is modified by the expansion of the 
apparatus—under pressures ranging between 77°3 and 77°6 cm. 
of mercury at 10° C.,! and their reduction to a common pressure — 
viz., that last mentioned. These reduced values I have taken a 
data. The temperatures are about 0:5°, 5°, 10° ete. to 45°, but 
frequently differ 0-1 or 0-2 from the whole number of degre 
The efflux times have consequently been corrected by interpol 
tion, having regard to second differences, so as to give their value 
for flow exactly at each fifth degree from 5° to 45°. These agail 
have been corrected for the fall in pressure at the entrance of the 
tubes, by formula (5) assuming m to be 1°12,” the results bel 
expressed to 0-1 second. The efflux times so corrected are ® 
follows :— 
sea aie ee a 
1 I do not remember that this is explicitly stated by Poiseuille, but 
may be observed that the values at 10° are those of the earlier e 
coe moir, and the method of reduction indicates what I have 
2 In § 8 it is mentioned that tube A indicated a value for m of 04a 
0'5, and that C, D, andE gave no satisfactory indication whatorer A of its 
value. Ihave not used this value for A because it depends on & 8" 
mination by three points only, and in the case of the other three ! ‘hi 
the correction mentioned is the most probable. : 
