On Fhidhif, and on the Structure of the Earth. 58 



In the restriction thus subjoined to his general position, 

 Lavoisier has adverted to the mediate operation of gravity in 

 maintaining the liquid state of bodies ; but he seems to have all 

 along overlooked the direct effect of the same power in the 

 maintenance of that condition of bodies. 



The difference of the three states of aggregation, solid, liquid, 

 and aeriform ; (for instance, ice, watsr, and steam), consists in 

 the circumstance of reciprocal attraction of component particles 

 counteracting their external gravity, as well as their own mu- 

 tual repulsion, in the one case ; and being overcome by those 

 concurrent forces (gravity and repulsion), though neither sepa- 

 rately surpass it, in the second ; while, in the third, repulsion 

 overpowers the mutual attraction of the particles, though it yet 

 does not likewise prevail over their gravity. 



The opposite conditions of a substance are the solid and the 

 gaseous ; determined by mutual attractionand by mutual repul- 

 sion of the particles. The mean state is that of transition I 

 when the two forces are exactly balanced. It is invariable as in- 

 dependent of external gravity and of its local variations. But 

 there is likewise an intermediate condition, which is that of a 

 viscous liquid, where gravity assists to overcome tenacity. 



A viscous or cohesive liquid differs from a non-viscid fluid, 

 as the mutual attraction of the particles is not counterbalanced 

 by their repulsion, though it is overcome by the further aid of 

 external gravity. The particles continue to cohere ; loosely, 

 however, so as their relative place in the assemblage or aggre- 

 gate are subject to be readily changed by an extraneous cause, 

 by gravity or by pressure. Their cohesion and consequent 

 maintenance of position are overbalanced by a repulsive force 

 and by gravity ; which, taken together, surpass the adhesive 

 force, though neither of them equal it separately. A solid, 

 whether viscous or brittle, is not alterable in respect of the re- 

 lative position of its component or integrative particles, by 

 the same causes unaided or unaugmented. Since their exter- 

 nal gravity, even acting in the same direction with the repulsive 

 energy, does not equal the cohesive force. A solid aggregate, 

 then, being upheld by extraneous matter, remains unchanged 

 in position in all its parts : a viscid liquid, upon a like support, 



