1833.] Attraction and Repulsion. 445 
when atoms are very near to each other.. From the great elasticity of 
gases, their atoms are treated of as beyond the sphere of mutual at- 
traction, and some philosophers* have accounted for the expansion be- 
ing equable for each equal addition of temperature, and for the ratio 
of expansion being the same in all gases, by the supposition of no at- 
traction existing between their particles, and as proofs of the non-exis- 
tence of any such attraction. How far this reasoning is correct let us 
presently examine. 
The elasticity of a gas is certainly no proof of the absence of any 
attraction between its atoms. It serves only to show that the whole 
repulsion is very powerful and superior to any attraction that may exist 
between its atoms. Since the attraction between the particles of a 
gas is inferior to the repulsive power, it cannot be apparent, though it 
may yet certainly exist. 
The gas will possess elasticity, and will expand unless subjected ta 
a compressing force, such as the atmosphere. 
Again, the equable expansion of a gas from each equal rise of tem- 
perature, is not any proof of the absence of attraction between its 
atoms on the ground usually taken, that if there were any attraction 
present, it ought, by decreasing as the atoms separated, and conse- 
quently offering less and less resistance, to allow of an increasing ex- 
q pansive effect from each equal addition of temperature. For it will 
presently be seen, that equal increments of temperature in gases by no 
means indicate equal quantities of heat, and therefore not equal addi- 
tions of repulsive power. Neither does the atmospheric pressure offer 
constantly equal resistance to the expansion of a gas; since asa gas 
expands this force tending to compress its atoms must increase, for as 
the particles of a gas recede from each other, each is subjected to and 
has to support the pressure of a greater number of 
a MM ! those of the atmosphere. ‘Thus in the annexed figure 
A.serseses B the line A B may be supposed to mark the contact of 
the atmosphere, anda volume of subjacent gas. Here, each particle 
of gas with its elastic mediumt, denoted by the dots A B, is subjected 
to the pressure of a column whose base is one particle of air. 
Let the gas be expanded by heat until the distance of 
AN the particles from each other is double. It is now clear, 
B that each particle with its elastic medium (now greatly 
* Murray, vol. i. p. 248, System of Chemistry. BrrrHoxuxrt, Chem. Statics. 
LAMBERT, vol. i. p. 116, 117, and 143. 
+ The seat of the repulsive force, according to most authors ; as will be pre- 
sently considered. 
