VISCOSITY OF WATER BY THE EFFLUX METHOD. 107 
dictum that n is about 6, were justified these means ought certainly 
to show a progression.: We conclude therefore that no general 
value, unless it be zero, can be assigned to mas assumed by 
Couette, that his deduction has been based upon an insufficient 
number of observations: hence no correction should be applied 
to the length of a tube unless experiments therewith clearly 
indicate its propriety. One would perhaps be hardly justified in 
declaring that » is in reality always zero, for the theory of the 
correction is rational, and there are experimental indications of, 
at least, its occasional validity : nevertheless in the absence of 
specific evidence as to its sign and magnitude in particular 
instances, there is no alternative but to disregard it. 
Viscosity of distilled water at 10° C. as determined from 
Poiseuille’s experiments with glass tubes. 
Tube. Expts. : x 105 R* X10" Length. - Tho 
Si Las 22 24284 10-030 ‘013074 
M* 37 002367 ~—-: 1850 3090 
c* Ls 42 3:2504 10-0325 3028 
D,* £8 44 23377 50225 3020 
B 56 10-235 10-005 3202 
Nae BO 57 «32659 7-495 3071 
E* 1.3 64 04716 2-31 3242 
A 70 = -24-941 ~—-10-05 3145 
Mean -013109 
e.g 75 10-276 7-505 3134 
F 85 11207: 38-3825 3147 
ee. ee 86 32980 4-97 3151 
ee 87 22787 «= -2B75 3078 
4,* 2-4 93 25059 7:58 3109 
oe oe iis 080s a a8r8 3070 
mee toe aS Gees OE 3119 
Ff, 163 11187: —-20-000 3065 
Mean -013109 
ea eee 
* We reject the last = as being uncertain in respect of the régime 
der w the flow too’ place. 
