VISCOSITY OF WATER BY THE EFFLUX METHOD. 17 
Tue HISTORY, THEORY, anp DETERMINATION oF THE 
VISCOSITY or WATER sy tHE EFFLUX METHOD. 
By G. H. Kyrsps, Lecturer on Surveying, University of Sydney.. 
[With Plate XI] 
[Read before the Royal Society of N. 8. Wales, July 3, 1895.) 
I.—History. 
II.—The Theory of Efflux. 
III.—Determination of the Viscosity. 
IV.—Indications for a further Determination. 
I.—Hisrory. 
1. The recognition of the existence of internal friction in fluids, 
and of its physical importance, was naturally followed by investi- 
gations to determine its amount. Each observer's measurements 
are in general, fairly consistent among themselves, but when 
compared with others, discrepancies are found ranging over some- 
what wide limits. This is true, even where the schemes of 
observation have been identical: where they have differed the 
divergence of results is very marked. 
In the case of water, the measure of the internal friction, 
expressed by the coéfficient of viscosity, has been deduced from 
observations of the following types, viz. of— 
(a) the decrement in the oscillations in U-shaped tubes : 
(6) the decrement in the oscillation of submerged dises : 
(c) the volumes of efflux from capillary tubes : 
(a) the decrement in the torsional oscillations about an axis of 
spheres filled with water : 
() the tangential force on the inner one of a pair of coiixial 
cylinders, exerted by the liquids lying between, when the 
outer one is rotated : 
(f) @ method similar to (e) the cylinders being replaced by 
sph 
In regard to the third method, (c), with which we are here 
more immediately concerned, it may be said, that although the 
