50 
‘above the fluid contained in the vessel, 
a column of this fluid. If we continue 
to elevate the disc, the column is length- 
ened; but, a period arrives, when its 
weight becoming superior to the adhesion, 
it is detached, and falls down. - The 
weight of this column, when it is about 
to fall, indicates the proportion of the 
resistance to be overcome, in order to 
- detach the disc; the analytical expression 
of which is-given by M. Laplace. 
When the fluid is of a nature to sink 
instead of rising in the capillary tube, 
the column supported assumes the form 
of a kind of truncated cone;-1n this case, . 
the analytical expression changes and in- 
cludes an additional element, that is, the 
angle, which the surface of the cone forms. 
with the disc of the glass. 
The first farmula, compared with the 
experiments of Messrs.Uauy and Achard, 
gives +; nearly the weight of the observed 
column. 
The second has not yet been compared, 
because it includes an angle, which ob- 
servers have hitherto neglected to con- 
sider; and of which it was equally 
difficult to foresee the importance, and 
to ascertain the proportion. 
If we place horizontally, one over 
the other, two dises of glass, leaving 
between them a very thm stratum of 
water, the two discs adhere together 
with a considerable force. M. Laplace 
gives on this occasion a formulas by 
which he finds the force. of adherence 
somewhat less than two-thirds of that-~ 
which M. Guyton had found by ex- 
periments. This difference doubtless 
depends on the very nice valuation of 
the interval which separates the disks; 
or perhaps the inequalities of ther sur- 
faces, which it is difficult to render per- 
fectly smooth. 4 
The same theory indicates a correction 
in the weil known hydrostatical prin- 
ciple discovered by Archimedes, respect- 
ing the diminution of weight which a 
body experiences when dipt into a liquid. 
This diminution cannot be estimated 
merely by the weight of a~volume of 
kiuid equal to the part of the body situated 
above the level. We must hkewise add 
to it the weight of the fluid removed by 
the capillary action, if the body is not 
of a nature to become moist; but if, 
on the contrary, it become moistened, 
we must subtract from it the weight of 
the volume raised up by the capillary 
action. M. Monge, in the Memoirs 
already cited, had ‘considered the first 
1 
Proceedings of Learned Societies. 
(Feb. J, 
part of this theorem as a thing perfectly 
evident. M. Laplace enters here into 
a rigorous demonstration of its truth, 
subjoining this reflection, that what. re- 
lates to the capillary action wholly dis- 
appears, when a body is completely im- 
mersed in a fluid beneath its level. 
To complete the explanation of cas 
pillary effects, M. Laplace considers, 
lastly, the curious phenomena which 
equal and very thin cylinders of steel 
exhibit when they swim on the surface 
of a fluid. In whatever manner we 
bring them into contact, they are not 
slow, after several oscillations, to unite 
throughout their length, as if they formed _ 
only one plate. These oscillations, being 
determined by analysis, it might be 
wished, that they should be observed 
with great accuracy, in order to compare 
them with their analytical expression. 
These comparisons, observes the author, 
are the touchstone of the theories; but 
in order that the proof may be'reckoned 
complete, it is not sufficient, that the 
formulz vaguely indicate the effects, 
which proceed from given circumstances ; 
it is moreover necessary, that they de- 
termine their exact quantities. M. La- 
place is about, we are informed by M. 
Delambre, to publish an interesting 
addition to thistheory. | | 
M. Roswag, of Strasburg, presented 
m 1784, to the Board of Commerce a 
kind of .gauze made of iron wire, for 
_which he received a premium, and the 
loom, which he had invented for its 
fabrication, was deposited in the cabinet 
of machines, at Vaucanson. 
Tn imitation of this fabric, M. Rochon 
produced others in 1799, which he var- 
nished with a transparent glue, in order 
to. substitute them for horn in the lanterns 
a-board ships of war. 
He is also of opinion, that this species 
of gauze covered with a thin coating 
ef plaster might protect ships and > 
buildings ashore from fire, or at least 
serve to render such .a calamity less 
frequent, and less destructive. 
These fabrics might in short prove 
extremely useful fur theatrical deco- 
rations, which are so liable to take fire; 
the only inconveniency attending their 
adoption, for such purposes, would be 
their want of flexibility; but M. Rochon, 
we learn from the present report, does’ 
not despair of discovering, by the aid 
of ‘chemistry, a remedy for’ this imper- 
fection; and it was chiefly with the view 
of obtaining the assistance of his learned 
associates, 
