684 
Exp. 17. If the preceding experiments with capil- 
lary tubes, excepting Exp. 9, be made in the exhaust- 
ed receiver of an air-pump, the fluids will rise to the 
same height as in the open air. 
Exp. \8. If the bore of a capillary tube be lined 
with a very thin coating of grease, or any unctuous 
substance, the water will not ascend in the tube. 
Exp. 19. By observing carefully the upper sur- 
face of the column of fluid, elevated in capillary 
tubes, it will be found to be concave upwards. M. 
Hauy found, that in capillary tubes of glass, of very 
small diameters, the concave surfaces of water and 
of oils differ very little from the form of a hemi- 
sphere. 
Exp. 20. If the capillary tube is taken out of the 
fluid in which it is immersed, and inclined to the ho- 
| rizon so that the included fluid may obey the action 
of gravity, the concavity will appear at both ends of 
the column, and suffers no variation either in its 
shape or size, whether the tube be held in a vertical, 
a horizontal, or an oblique direction. 
Exp. 21. When the column of water is thus made 
to move along the tube, it seems to suifer a resist- 
ance as it approaches to either end, and it does not 
completely reach the extremity of the tube till the 
tube is almost inverted. 
Exp. 22. When a capillary tube is immersed in 
mercury, or in any metal in a state of fusion, the 
fluid, instead of rising, is depressed in the tube below 
the general level. See Pg. 4. 
Exp. 23. If a drop of mercury be introduced into 
a conical capillary tube, held in a horizontal position, 
the mercury will move towards the wide end. 
Exp. 24. By observing the surface of a column 
of mercury depressed in a capillary tube, or enclosed 
in a barometer tube, it will be found to be convex 
upwards. Mr. Hauy has endeavoured to show, that 
this convexity differs very little from the form of a 
hemisphere. Dr. T. Young maintains that this re. 
sult is inaccurate, and that the angle formed by the 
surface of the mercury with the side of the tube is 
140°. 
Exp. 25. When the mercury and the capillary 
tube are perfectly dry, the fluid will rise above the 
general level, like all other liquids. By drying the 
mercury and the tube to a very great degree, Messrs. 
La Place and Lavoisier constructed barometers, in 
which the mercurial column was terminated above 
by a plane surface, and they even succeeded in ren- 
dering the upper surface of the mercury concave. The 
observations given under Exp. 24 are referable to 
barometers constructed in the usual way. 
Exp. 26. If two plates of glass be placed parallel 
to each other, at the distance of about 73, of an 
inch, the water in which they are immersed will rise 
one inch above its level in the vessel; and when the 
plates are placed at different distances, the heights 
to which the water will rise, will be reciprocally 
proportional to the distances of the plates. 
Exp. 27. Vf a capillary tube be taken of such a 
magnitude that the diameter of its bore is equal to 
the distance between the plates in the preceding ex- 
periment, the water will rise in it to the same height 
as between the plates. 
Exp. 28. If a fluid is either elevated or depressed 
between two vertical and parallel planes, the planes 
will tend to approach each other. 
Exp. 29. ‘If two plane polished plates of glass, 
three or four inches broad, and twenty or twenty- 
five long, be laid one of them parallel to the horizon, 
the other upon the first, so as at one of their ends to 
touth one another, and contain an angle of about 10 
or 15 minutes, and the same be first moistened on 
their inward sides with a clean cloth dipped into oil 
of oranges, or spirit of turpentine, and a drop or two 
of the oil or spirit be let fall upon the lower glass at 
the other end; so soon as the upper glass is laid down 
CAPILLARY ATTRACTION, 
upon the lower, so as to touch it at one end as above, 
and to touch the drop at the other end, making with 
the lower glass an angle of about 10 or J5 minutes; 
the drop will begin to move towards the concourse 
of the glasses, and will continue to move with an ac- 
celerated motion till it arrives at that concourse of 
the glasses. For the two glasses attract the drop, 
and make it run that way towards which the attrac- 
tions incline. And if when the drop is in motion, 
you lift up that end of the glasses where they meet, 
and towards which the drop moves, the drop will 
ascend between the glasses, and therefore is attract- 
ed. And as you lift up the glasses more and more, 
the drop will ascend slower and slower, and at length 
rest, being then carried downwards by its weight as 
much as upwards by the attraction. And by this 
means you may know the force by which the drop 
is attracted at all distances from the concourse of the 
glasses. Now, by some experiments of this kind, 
it has been found that the attraction is almost reci- 
procally in a duplicate proportion of the distance of | 
the middle of the drop from the concourse of the 
glasses, viz., reciprocally in a simple proportion, by 
reason of the spreading of the drop, and its touching | 
each glass in a larger surface; and again reciprocally | 
in a simple proportion, by reason of the attraction 
growing stronger within the same quantity of at- | 
tracting surface. The attraction therefore within 
the same quantity of attracting surface is reciprocally 
as the distance between the glasses. And, there- 
fore, where the distance is exceeding small, the at- 
traction must be exceeding great.” Vewton’s Optics, 
p. 367. # 
Exp. 30. If the plates in Exp. 26 are inclined to | 
each other at a small angle, and are immersed in 
water with the line of their intersection vertical, the |. 
water will ascend between them, and will form a 
beautiful curve. 
Fig. 6. 
Dr. Hooke, who was one of the earliest writers | 
on capillary attraction, ascribed the ascent of 
fluids, in capillary tubes, to the unequal pressure 
of the atmosphere, arising from a diminution of 
the pressure of the air in consequence of its 
friction in the tube. This opinion was main- 
tained till the experiment was tried in the re- | 
ceiver of an air-pump, and when the fluid was 
found to rise as high in vacuo as in the open air, 
a new cause was sought for the phenomenon. 
Sir Isaac Newton and Mr. Hauksbee were of 
opinion, that the attraction of the tube was in- _ 
Dr. Jurin ascribed | 
sensible at sensible distances. 
the suspension of the fluid to the attraction of 
the ring of glass to which the upper surface 
of the water is contiguous, and adheres. Dr. 
Hamilton and Dr. Matthew Young maintained, 
that the fluid was elevated by the lower ring of 
glass contiguous to the bottom of the tube, and 
that this ring raises the portions of fluid imme- 
diately below it, and then the other portions in 
succession, till the column thus elevated was in 
equilibrium with the attraction of the ring. 
Clairaut had the honour of being the first 
mathematician who gave any thing like a theory 
of capillary attraction. After pointing out the 
insufficiency of preceding theories, he enters 
into an analysis of all the forces by which the 
fluid is suspended in the tube, of which we shall 
endeavour to give our readers a brief account. 
Let ABCDEFGH, fg. 7, be the section of a ca- 
This experiment is represented in | 
