56 On Fluidift/, and 



into interstices by any other cause produced. The permanent 

 elasticity then of a substance, within which heat exercises its 

 repellent power is limited by the attainment of that uniform 

 diffusion. 



A certain dose of heat, augmenting a low and overpowered 

 degree of repulsion, until by the aid of gravity it balances mu- 

 tual attraction, reduces a solid substance to a viscous state, which 

 it retains during subsequent increments of heat, so long as tena- 

 city is not outdone by repulsion singly. A further dose of heat, 

 increasing repulsion till it equals the mutual attraction of the 

 particles, perfects their mobility ; and the next addition makes 

 the liquid pass into the elastic form of vapour ; and further ac- 

 cession of heat enables it to overcome the pressure of a superin- 

 cumbent elastic mass, and penetrating it, take a place there suit- 

 able to the degree of the elasticity. 



The stages of transition from solid to vapour may be brought 

 into one view in a compendious manner, by a notation and ex- 

 pression borrowed from algebraic symbols. 



Thus let a represent attraction of the particles for each 

 ether, r, repulsion between them ; g, gravity, or attraction of 

 the earth's mass. Then a y r, denotes tenacity; and a Z. r, 

 elasticity ; and a __ r -^ g signifies the solid state of a sub- 

 stance ; a y r yet /. r + g, the tenacious liquid; a ^. r, the 

 perfectly mobile liquid, and point of transition from the tena- 

 cious liquid to the gaseous state ; a Z »' (but a -\- g y r) the 

 gaseous form ; a + g ^ r, the limit of a terrestrial elastic 

 fluid or gas ; and, lastly, a + g /. r &a unrestrained elastic 

 fluid. 



In any of these expressions, if one of those quantities vary, 

 another will vary likewise. Thus, if g be taken as variable, as 

 in truth it may, since it differs with the latitude of the place, and 

 elevation of position, then r being constant, a will vary, and the 

 adhesive attraction, which uniform repulsion can overcome, is 

 greater or less, as the gravity of the substance differs. So, 

 making a constant, r will vary ; and the quantity of repulsion 

 (or heat, which is the occasion of it,) that is requisite to over- 

 power adhesive attraction, is increased or diminished with the 

 difference of gravity. 



