SiGERSON — Buoyancy of Bodies Denser than Water. 25 



reasons, a very tangible and noteworthy force, which cannot be elimi- 

 nated from consideration, in such and similar problems, without inac- 



CUXSlCJ. 



This being so, it may become necessary to revise certain definitions 

 or statements of laws in physics, in order that the presence of this force 

 may be recognised where it exists. Thus, it is mentioned that a float- 

 ing body is acted on by two forces — its weight, and the resultant of 

 fluid pressure. To this it may be necessary to add, that a third force, 

 adhesion of air, exists, and becomes a perceptible agent in the case of 

 small floating bodies. 



Again, in the curving of liquids in contact with solids, the presence 

 of air is altogether unrecognised, and only the forces acting through 

 the visible media are mentioned. Thus we are told that when a solid 

 is placed in a liquid which wets it, the liquid, as if not subject to the 

 law of gravitation, rises against the side of the solid and becomes con- 

 cave. It is added that where the solid is not wetted by the fluid, the 

 latter is depressed and becomes convex. Now, it appears to me, from 

 the foregoiog facts, that this should be re-stated in the following manner : 

 When an aerated solid is placed in a liquid whose adhesive power is 

 greater than the adhesive power of air, as regards such solid, the air 

 is partially displaced, the fluid becoming concave and the air convex. 

 But when an aerated solid is placed in a liquid whose adhesive 

 power is less than the adhesive power of air, as regards such .solid, 

 then the water is partially displaced by the air and becomes convex, 

 whilst the latter grows concave. The concave, in either case, bounds 

 the outward side of a wedge of advancing substance, whose inner side 

 is applied to the solid. 



It follows that it would probably be well to modify the manner in 

 which the first law of Gay Lussac is expressed, in order to recognise 

 the presence of air-adhesion as a power. As it stands, the law is : 

 ''When a capillary tube is placed in a liquid, the liquid is raised or 

 depressed according as it does or does not moisten the tube." I would 

 read it thus : " When a capillary tube is placed in a liquid, the liquid 

 is raised or depressed according as its adhesive" power is greater or less 

 than that of the air." 



These suggestions are oflfered, with diffidence, to the consideration 

 of physicists, as there may, in such cases, be forces operative which 

 have not yet come under review. But, lest I should be supposed to 

 have overlooked the obvious objection that Gay Lussac's law is said to 

 hold good in vacuo, and therefore in the absence of air, I must add 

 that it is confessed that the air-pump gives no absolute vacuum. 



The air becomes exceedingly rarified, but a perceptible quantity is 

 left. And, when it is remembered that, from the facts now experi- 

 mentally demonstrated, it was shown that the adhesion of air to a 

 solid, in a given case, is greater than the adhesion of air-molecules 

 between themselves, it will be admitted that the instruments used in 

 an air-pump may be covered with an adhering film of air, until dis- 

 placed by water, operative in causing the phenomena recorded. 



K. I. A. ruOC. — SEU. II., VOL, II., SCIKNCE. E 



