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 obtuse, 

 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 acute the angles of inchnation are, the 

 greater will be the extent of surface which the attracting substance 

 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, in my view, established the following laws. 



1st. 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 tlieir greatest degree of attraction may be knoAMi by 

 tlie angle which will, in given circumstances, sustain an elevation of 

 any hquid, except some liquids that, by attraction spread on the sur- 

 face of other Hquids, 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 a 

 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. 



