44 PHYSICS. 
convexity and concavity being equal to the inner diameter of the tube 
The regularity of this structure, however, depends entirely upon the clean- 
ness of the inside of the tube. : 
If a capillary tube which has been employed in any of the above- — 
mentioned experiments be raised out of the liquid, the liquid originally 
contained therein will be retained there by the pressure of the atmosphere, 
and a drop which may have been suspended to the lower end will even be 
driven inside; and with sufficiently thin walls, the height of the column of 
liquid may thereby be raised to nearly double the original amount. 
Syphon tubes exhibit similar phenomena; and in concentric tubes the phe- 
nomena of capillarity take place in the inner tube and the ring between the 
two, as if each one alone were present. If, therefore, the diameter of the 
tube be twice as great as the thickness of the tube, the summits of the 
columns will be equally high in both. Parallel plane plates may be con- 
sidered as parts of infinitely great concentric tubes, and experiment has 
shown that the phenomena of capillarity are precisely the same in the two 
cases. Ifthe plates are inclined at a very acute angle, as in pl. 18, fig. 22, ° 
ADBE and CDBF, the liquid in the narrow part will rise higher than in 
the wider, and in such proportion, that the areas of the rectangular trans- 
verse sections, as ab and cd, are always equivalent. The shape of the 
curve, DE, forming the outline of the fluid, is that of an equilateral hyper- 
bola, whose asymptotes, on the one hand, represent the line of intersection 
of the plates, and on the other, the level of the liquid. If the plates be 
removed from a vertical position to a horizontal, and a drop of water be 
interposed, it assumes a circular form, and passes to the line of intersection 
of the plates, and this with a rapidity greater in proportion to the sine of 
the included angle. Similar phenomena are exhibited by conical tubes. 
The small column of liquid, mm’, moves towards the point of the tube, as 
in fig. 23, and towards the broad end, as in fig. 24, and in the two cases 
assumes either a convex or a concave outline. 
As a general rule, solid bodies cannot come in contact with fluid without 
the surface of the latter experiencing a greater or less change. Particu- 
larly remarkable in this respect are the phenomena of attraction and 
repulsion presented by bodies swimming in liquid. Two balls swimming 
in liquid and moistened by it, as balls of cork in water, when within suffi- 
cient proximity, attract each other with considerable intensity (fig. 25) ; 
likewise, two balls not moistened, as of wax (fig. 26). On the other hand, 
two balls repel each other when one is moistened and the other not (fig. 
27). Similar phenomena are presented by vertical plates (figs. 28 to 30). 
Another of the phenomena of attraction is the adhesion of plates to the 
surface of water, so that when they lie horizontally upon this surface, they 
can only be raised by the exertion of a greater or less force. The amount 
of this force is dependent upon the density of the fluid, increasing with this 
density. The material of the plate produces no difference in the result. 
We cannot here go into an elucidation of the theory of capillarity, but 
will only remark that, according to the most recent theory of Mile, capil- 
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