90 Inquiries into the Principles of Liquid Attraction. 
sidered an element ; but Chemists, by subjecting it to the test of a 
rigid analysis, have ascertained its composition ; and it is by the help 
of some appropriate experiments, that we must acquire a knowledge 
of its attracting powers. 
The practice of washing wheat, to free it from smut, has present- 
ed, on this subject, some facts, worthy of attention. In the process 
of washing, when the tub containing the wheat and water is inclined 
for the purpose of pouring off the water, many of those grains which 
are just above the water, float out and cover the surface, and re- 
quire to be constantly beaten down to make them sink, and to prevent 
them from running off with the water. These grains of wheat, com- 
pared with the water, are specifically heavier, and yet they float, as 
in the case of the globules of mercury, abovementioned ; not be- 
cause, as some have supposed, they are specifically lighter than wa- 
ter, but because the obtuse angles, which their convex surfaces make 
with the surface of the water, cause a depression around them. 
Again, when the wheat is emptied by inverting the tub, some of 
the grains usually adhere to the sides of the tub, by means of the 
aqueous surface which surrounds them ; and thus they are suspended 
by an attracting force, much greater than their own weight. But i 
we again fill the tub with water, these grains of wheat sink as soon 
as the water rises above them. This fact proves that the attracting 
force which suspended them is destroyed, when the grains are sub- 
merged. The needle, also, when wet, will adhere to the side of a 
tumbler, above the water ; but only raise the water above the needle, 
by inclining the tumbler, and the needle sinks. 'These facts evince 
that the surface of the liquid is the seat of the attracting power. 
For the properties of the attracting power, we must look to the 
soap bubble as it stands on a liquid, the bubble of pure water being 
too evanescent for inspection. This soap bubble presents to us a 
thin coat of particles, apparently very uniform in thickness, impervi- 
ous to air, of uniform strength, and equally contractile in all its parts.* 
* By “ contractile,” is meant that constantly uniform strain, which may be ob- 
served eee the particles of the surface, and by which the surface has a tendency 
to shor If. 
pattie re way of illustration, when globules of mercury have been flattened by 
pressure, and have thus had their Surtaecs enlarged, their globular form is 
stored by the contracting power of the surface, as soon as the pressure is removed ; 
‘and when drops of water, on cabbage leaves, have had their surfaces enlarged in the 
Ss way, they will again resume their spherical ae for the same reason that the 
globles of mercury did, on removing the pressure 
