88 Inquiries into the Principles of Liquid Attraction. 
needle, and three or four times its weight, and balancing it over the 
edge of a tumbler full of water. (See Fig. 15.) The acute angles 
which the convex surface of the needle makes with the surface of 
the liquid, elevate the liquid, and support the piece of wood over 
the outside of the glass; and when the needle only is placed on 
water, it descends into the water till the angles are sufficiently obwse, 
and then the liquid is depressed, and the needle swims. (See Fig. 16.) 
The cause why these different angles elevate the surface of the 
liquid, is this. The more aeute the angles of inclination are, the 
greater will be the extent of surface which the attracting substence 
presents to the surface of the liquid; and the consequence is, that 
the extent and force of the focal seat of attraction, from which the 
elevating power acts, is increased. By “ focal seat of attraction,” 
is meant, the line where the surface of the liquid comes in contact 
with the surface of the attracting substance; and it is called focal 
seat because the mutual attraction which exists between the two sur- 
faces, and which causes the elevation, is concentrated in this place. 
A careful observation of the above experiments, and many more 
of a similar kind, has, ia my ‘view, established the following laws. 
Ist. The common surface of a liquid never rests in a horizontal 
position when it comes in contact with any substance ; but is always 
either elevated or depressed. It may be observed that there is a 
striking analogy between the angles of these opposite curves of ele- 
vation and depression. ‘They seem to bear some resemblance to 
those of a parabola. 
2d. Different substances have different degrees of attraction for 
liquids; and their greatest degree of attraction may be known by 
the angle which will, in given circumstances, sustain ap elevation of 
any liquid, except some liquids that, by attraction spread on the sur- 
face of other liquids, as oils on water, and are not elevated. 
3d. All substances attract liquids more readily when moistened 
with the same liquid, than when dry, for those bodies that have @ 
weak attracting surface, are by this means furnished with a strong 
attracting surface. But when grains of wheat, and globules of mer- 
cury are moistened, they will, notwithstanding, float; for after they 
have been shaken to the bottom of a liquid, they will again float, 
when raised to the surface. 
4th. Two bodies floating on a liquid, both of which are attended — 
by an elevation of the liquid, will, when near, approach each other — 
with a column of liquid rising between them. 
