186 G. H. KNIBBS. 
Nore on RECENT DETERMINATIONS or tHe VISCOSITY 
F WATER sy tHE EFFLUX METHOD. 
By G. H. Kwyipss, F.R.A.8., L.8., - 
Lecturer in Surveying, University of Sydney. 
[Read before the Royal Society of N. S. Wales, September 2, 1896.] 
1. Ina paper on the above subject,! read before this Society 
3rd July last year, reference was made (Note 4, p. 132) to the 
viscosity measurements of Thorpe and Rodger. These, since to 
hand,” give two series of values for the viscosity of water, one 
between the limits 0° and 100° C., the other between the limits 
0° and 8° C., the latter being obtained in order to ascertain 
whether the viscosity curve shewed any peculiarity at the tem- 
perature of maximum density. I propose, therefore, to briefly 
consider how far their determinations, and those of other investi- 
gators whose work was previously overlooked, modify the results 
given in my paper; and thus, by completing the review of the 
subject, to indicate the present state of knowledge in regard to 
the evaluation of the viscosity constant for water. 
2. Theory of Correction of Presswre.—Contemporaneously with 
the publication of Couette’s deduction, that the pressure head in 
the reservoir supplying the efflux tube, should be reduced by the 
amount U/?/g, Gartenmeister® stated that Finkener had, in an un- 
published treatise, shewn that that correction was the proper one. 
In 1891 Wilberforce* pointed out the principal defect in Hagen: 
bach’s reasoning, which led the latter to adopt the coéfficient 2 ah 
for the value of m in the equation 
t Journ. Roy. Soc. N. 8. Wales, Vol. xxrx., pp. 77 — 146, 1895. 
2 On the relations between the viscosity of liquids and their chemical 
nature.—Phil. Trans. Vol. 185, Pt. 2, pp. 397 — 710, 1895. 
3 Zeitschrift fiir physikalische Chemie, Bd. 6, p. 524, 1890. 
4 On the calculation of the coéffivient of viscosity of a liquid from its 
rate of flow through a capillary tube—Phil. Mag. Ser. 5, Vol. 31, PP- 
407 - 414. 
