and the Molecular Forces of Fluids. 95 
the fluid surface will be the least possible, and the column 
may be considered to be supported by the action of the fluid 
on itself. The fluid will thus hold the place of the solid in 
the equation previously obtained; we shall have q' = 4, and 
the equation will become 
gsing = gcos¢ +k. 
Hence, on account of the smallness of g and & compared to 
g, the angle of contact with the aqueous tube will be small as 
well as of that with the solid. Consequently the intermediate 
angle » will be small, and the heights of ascent be the same 
whatever be the solid, if the fluid thoroughly wets it. In the 
experiments of M. Link, (see Poggendorfi’s Annalen 1833, 
p. 404,) the condition here supposed was fulfilled by means 
of an apparatus for dipping the solid repeatedly in the fluid. 
The height of ascent is found to be independent of the nature 
of the solid, or nearly so. In subsequent experiments, (Pog- 
gendorff’s Annalen, 1834, p. 5935) the plates between which 
the fluids ascended were previously dipped in strong caustic 
alkali and concentrated sulphuric acid, to get rid of a film of 
grease attaching to them, which they contract in the act of 
polishing. Water, in these new experiments, stood very 
nearly at the same height between glass, copper, and zinc 
plates. Other fluids did not follow this law, and in the in- 
stance of sulphuric acid, the deviation appeared to depend on 
a chemical action between the solid and fluid. Such a cir- 
cumstance would be likely to affect the form of the curve 
ANQ and angle », and consequently, according to the 
theory, the height of ascent. 
The general inference from the foregoing reasoning is, that 
the heights of ascent do not merely depend on the molecular 
attractions, but, while these remain the same, may be affected 
by any circumstance that alters the form of the fluid surface 
near the solid, and particularly by the manner and degree of 
moistening the solid by the fluid. In this way the differences 
of the heights, as determined by different experimenters, may 
be accounted for. 
The maximum height of ascent in a given tube varies, ac- 
cording to theory, for different fluids, as a certain quantity 
—, in which ¢ is the specific gravity of the fluid, and H* de- 
g 
* This is the quantity called H by Poisson, and by Laplace in his Sup- 
plementary Treatise. The quantity so denominated in Laplace’s first 
Treatise is equal to —. This letter is inadvertently used sometimes in 
one of these senses, and sometimes in the other, in the Report on Capil- 
lary Attraction, 
