24 Proceedings of the Royal Irish Academy. 



3. The body may take with it adhering air siifiicient to serve as 

 counterpoise (if I may use the words) to its own weight in water, aud 

 thus it may float completely immersed in the water, surmounted by an 

 air-globule. 



4. The amount of air adhering may be so great as to prevent the 

 complete descent of the body, to hinder it from diving much below the 

 surface, and to rapidly draw it up again to the surface. In such a 

 case, the adhesion of the air to the object is evidently sti'ong enough 

 to completely resist the weight of the object in water, and to partially 

 resist the force acquired by a fall from a distance, relatively con- 

 siderable. 



The air-adhesion may be broken in, at least, three ways. Pirst, 

 by the blow the object receives on striking the surface in its descent, 

 so that it may go down without any globule, or if the effect be partial, 

 with a small one. Second, by the blow received on reaching the bottom. 

 Third, by the shock when, rising to the surface, the air globule suddenly 

 expands. On account of the narrowness of the base of connexion, in 

 some cases, the adhesion may be quietly severed, by water-pressure. 



In cases where a body is quite buoyant in the water, on account of 

 the attached globule, it may be readily shown that the base of con- 

 nexion forms an adhesion area large enough to sustain this body at the 

 surface, when the upper air shall replace the globule. This is demon- 

 strated, as in case 2, by gently elevating the body to the surface, and 

 allowing the globule to open into the upper air : or, by observing, as 

 in cases 3 and 4, the ascent of bodies drawn up by their globules to 

 the surface, where, if the shock of the expansion of the globule do not 

 sever the adhesion, they will float. In such cases, the area of aerated 

 space remaining the same, the adhesion of the upper air now manifestly 

 sustains the body in a buoyant state. 



In this condition buoyant bodies, whose density is greater than 

 water, present themselves usually to observers. From the facts related, 

 it follows that they are sustained in this position, partly by the ad- 

 hesion of the atmospheric air. 



The incidents of this demonstration suggest some remarks and infe- 

 rences. When we withdraw a glass rod or a wetted body from water, 

 the drop which adheres shows that in such cases the force of adhesion 

 between the liquid and solid is greater than the force of cohesion be- 

 tween the molecules of the liquid. Conversely, when we let pass an 

 aerated body from the air into the liquid, the globule or drop of air 

 which adheres to it, proves that, in such cases, the force of adhesion 

 between the gas and the solid is greater than the force of cohesion 

 between the molecules of the gas. We have seen that it is also strong 

 enough, in certain cases, to sustain a Avcight as great as, or greater 

 than, the weight of a given body, minus the weight of the volume of 

 water displaced, and that it is potent enough to resist the action of the 

 forces which, when a hodj is let fall from a height into water, tend to 

 separate globule and body, sending the former upwards and the latter 

 down. 



The force of adhesion between air and solid is, therefore, for many 



