12 Prof. Leslie on Heat and Climate. [July, 



jacent matter arising from approximation observed the same pro- 

 portion with their repulsion, a body would be capable of imbib- 

 Hig any quantity of heat, without emitting it in the form of 

 lio-ht. "But after a certain accumulation of heat, the balance is 

 destroyed ; and as nature admits only gentle transitions, we 

 may reasonably conclude, that the attractive power increases 

 regularly at a slower rate than the repulsive. The attraction of 

 the particles of matter to each other, which is the third force 

 necessaiy to the general quiescence, appears in all ordinary 

 cases to be exactly proportional to the quantity of dilation : for 

 a solid body yields the same musical note with whatever violence 

 it is struck ; this is likewise true of air, and other similar fluids, 

 and is the principle of wind instruments ; and the experiments 

 performed in the receiver of an air-pump evince that the expan- 

 sion of water and other fluids corresponds precisely to the pres- 

 sure removed. The distention of a body being the measure of 

 the mutual attraction of the particles of matter, is a certain 

 proof that the combined light is in a condensed state. But this 

 distention will not be the same in all bodies, since the attrac- 

 tion occasioned by a certain derangement differs in each. 

 Even, in the same body, equal additions of heat applied suc- 

 cessively will not produce uniform expansions, which must have 

 been the case if the attraction of the luminous particles to 

 matter increased at the same rate with their mutual repulsion ; 

 but as the latter force begins to exceed the former, it occa- 

 sions a further dilatation. We may, therefore, state it as a gene- 

 ral principle, that the expansions produced by equal accessions 

 of heat, form a rising progression. Mercury discovers this pro- 

 perty ; spirits of wine indicate it in a more remarkable degree ; 

 -and the expansions of water between the freezing and boiling 

 points correspond to the series of square numbers. It is true 

 that equal increments in the longitudinal dimensions would be 

 attended with progressive augmentations of volume : thus the 

 differences of the cubes of 10, 11, 12, 13, &c. are the numbers 

 331, 397, 469, &c. But this consideration is insufficient for 

 the great anomalies observed. The above principle will explain 

 other facts that appear to have no immediate dependance on 

 it. The contraction, for instance, which a given pressure 

 produces on cold water is greater than that on warm ; inso- 

 much that the effects at the temperatures of 45° and 65°, I 

 find to be nearly in the proportion of 4 to 3. The reason 

 seems to be this : — In the accumulate state of the igneous 

 fluid, a certain condensation occasions a considerable excess 

 of the repulsive above the attractive powers, and thence arises 

 a dilatation which diminishes the equal contraction that other- 

 wise would take place. 



Our views lead also to another curious inference, namely, 

 that a body which emits light copiously is in its state of the 

 utmost distention. Hence this emission will not be conjoined 

 with the same temperature in all bodies; the more dilatable 



