On Laplace's Theory of Capillarity. 339 
such preeminence may not exist ; but I do not think that it is 
here made conspicuous. 
My friend Prof. Chandler Roberts has for a long time been 
engaged in studying the diffusion of melted metals, and the 
matter has been a subject of frequent conversation between us. 
I await with great interest the details of his experiments. The 
relative dates of our publication have no relation to the dates of 
our experiments. 
XL VII. On Laplace's Theory of Capillarity. 
By A. M. WORTHEsGTOsj M.A. 
To the Editors of the Philosophical Magazine and Journal. 
Gentlemen, 
rpHE appearance of Lord Rayleigh's paper on Laplace's 
J- Theory of Capillarity encourages me to send you some 
remarks on the same subject which I had prepared some months 
ago in connexion with work on capillarity on which I have been 
engaged. I should be glad, however, that it should appear on 
the present occasion, as I think it may be of some use in 
explaining, rather more explicitly than Lord Eayleigh attempts 
to do, how the misconception of Laplace's quantity K ha3 
arisen — a misconception which has become of almost historical 
importance in connexion with this subject. 
The object with which Laplace sets out is to explain the 
fact that the hydrostatic pressure in a liquid just below a 
curved surface differs from the hydrostatic pressure just below a 
plane surface by an amount depending on the curvature of the 
surface. 
He gives the accompanying figure, representing a vertical 
section of a capillary tube NB 
plunged in a vessel A C con- 
taining a liquid which wets the 
tube. 
V R Z represents an infi- 
nitely thin canal or filament of 
the liquid whose cross section 
is taken as the unit of area, and 
which meets the plane surface 
at V and the curved surface at 
its lowest point 0. On the as- 
sumption that the fluid is of uni- 
form density throughout, and 
that between any pair of ele- 
mentary volumes of it there is an attraction which is a function 
2B2 
N 
M 
K 
\ 
> 

/ __— -^ 
^_ 
1 
F 
E 
\ 
? 
