ADHESION

, Adherence, in Physics, is the state of two bodies, joined or fastened together, whether by mutual attraction, the interposition of their own parts, or the impulse or pressure of external bodies. See Cohesion.

Thus two hollow hemispheres, exhausted of air, are made to adhere firmly together by the pressure of the atmosphere on their convex or external surfaces; for if they are introduced into an exhausted receiver, they presently fall asunder. Also two very well polished | planes adhere firmly together, partly by the external pressure of the atmosphere, and partly by the attraction of their parts.

In No. 389 of the Philos. Trans. Dr. Desaguliers has given experiments of the adhesion of leaden bullets to each other: the cause of which he resolves into the principle of attraction.

M. Musschenbroeck, in his Essai de Physique, has given a great many remarks on the adhesion of bodies, and relates various experiments which he had made upon this matter, but chiefly relative to the resistance made by bodies to fracture, in virtue of the adhesion of their parts; which adhesion he ascribes principally to their mutual attraction. Common experiments prove the mutual adhesion of the parts of water to each other, as well as to the bodies they touch. The same may be said of the particles of air, on which M. Petit has a memoir among those of the Paris Academy of Sciences for the year 1731.

Some authors however are not willing to admit that the adhesion of the parts of water, or indeed of bodies in general, is to be attributed to the attraction of their parts, and they reason thus: suppose, say they, that attraction acts at any small distance, as for example to the distance of one-tenth of an inch, from a particle of water: and about this particle describe a circle whose radius is one-tenth of an inch: then the particle of water will be attracted only by the particles included within the circle; but as these particles act in contrary directions, their mutual effects must destroy one another, and there can be no attraction of the particle, since it will have no more tendency one way than another.