Inquiries into the Principles of Liquid Attraction. 91 



It partakes of all substances which are mixed or dissolved in the 

 liquid ; but it differs essentially both in its mechanical properties, and 

 in its appearance, from the liquid state in which it previously existed. 

 This coat of particles, of which the bubble is constituted, is sustained 

 by the enclosed air ; and it has an elevation of the liquid at its base, 

 where it unites with the surface of the liquid ; and it may be consid- 

 ered a mere continuation of this surface. Like other attracting 

 bodies, it approaches those which have an elevation of the liquid, 

 and avoids those which have a depression ; but unlike muscular fibre, 

 it has no corrugation, but its particles at all times exert the same 

 steady contracting force. Such, I conceive, is the nature of the sur- 

 face of all liquids 5 and it is this contractile power which it has, that 

 causes the drops of a liquid to assume a spherical form. 



Again, those particles beneath the contractile surface are, emphati- 

 eally, liquid. They move over each other without cohesion, or 

 sensible resistance, and may be considered passive, except so far as 

 they are subject to the law of gravitation. 



The reason of this remarkable difference between particles of the 

 same liquid, without supposing any chemical change to have taken 

 place in any of them, must be attributed to the different situations 

 and circumstances in which they are placed, one class of them con- 

 stituting the surface, and the other the liquid beneath it. The par- 

 ticles of the surface have no external particles of the same kind to 

 balance them, or to counteract their attraction for each other ; where- 

 as, those beneath the surface, being entirely surrounded by particles 

 of the same kind, have their attractive forces equally balanced in 

 every direction, and by this means are kept in equilibrium, and pos- 

 sess hydraulic properties. And this I conceive to be the great cause 

 of difference between the particles of the surface, and the particles 

 beneath it. 



Some estimate may be made of the strength of the surface of dif- 

 ferent liquids, by observing the magnitude of the largest drops which 

 their contractile power will enable them to retain in a spherical form, 

 when resting on substances which have for them the least attraction, or 

 when suspended under bodies which have for them the greatest at- 

 traction. (See Figs. 6, and 7.) 



Having pointed out the seat and properties of liquid attfaction^ 

 some attention will now be directed to its various applications. 



1st. To its application in explaining the phenomena connected 

 with the first law, above mentioned, viz. : " that the common surface 



