Inquiries into the Principles of Liquid Attraction. 87 



Fig. 4.) Two of these globules, when brought within the distance 

 of about an inch of each other, rushed together with a force which 

 was constantly increased as they approached. (See Fig. 5.) These 

 globules produce a very sensible depression of the liquid, and equally 

 avoid the pin and the sides of the cup. 



These experiments were ail made about twenty years since, and 

 from that period, ray inquiries have been occasionally directed to the 

 discovery of those substances which are attended with an elevation 

 of the hquid around them, and to those which have a depression. In 

 my first experiments, vegetable leaves seemed to depress liquids, 

 and glass and metals to elevate them 5 but by giving them differ- 

 ent positions, and consequently different angles of inclination to 

 the surface, I discovered that all substances, when their angles of in- 

 clination are sufficiently acute, are attended with an elevation of the 

 liquid ; and when sufficiently obtuse, with a depression. A green 

 vegetable leaf, placed perpendicularly in water, has on both sides a 

 depression, but give the leaf a suitable inclination to the surface, and 

 the liquid is elevated on the side of the acute angle, and depressed 

 on the side of the obtuse angle. 



A fine needle, also, carefully placed on water, is known to swim. 

 Now the convex surface of the needle, (the needle being considered 

 a cylinder,) presents no difference of angles to the surface of the 

 liquid, on its revolving. By the angles which the convex surface 

 makes with the surface of the liquid, is meant, the angles which are 

 made with the surface, by the tangents, drawn to all the different 

 points in a circular ring, taken about tlie needle, and produced to 

 meet the surface of the hquid. For it is well known that a line from 

 any point in this circular ring, makes the same angle with the surface 

 of tlie hquid, which the tangent of that point makes with the same 

 surface. The same explanation is also applicable to the convex 

 surfaces of the globules of mercury. But when these globules, or 

 the needle, descend into the liquid, the tangents of these convex 

 surfaces, and consequently the convex surfaces themselves, make all 

 the varieties of angles with the surface of -the liquid, first the acute, 

 and then the obtuse 5 and, as it has already been remarked, when 

 any substance makes angles vvith the surface sufficiently acute, it is 

 always attended with an elevation of the liquid ; and whenever suffi- 

 ciently obtuse, with a depression. This is tlie case in the descend- 

 ing of the needle ; and it is proved to be the case, by inserting the 

 point of a needle in a small piece of wood, of equal length with the 



