Dr. Woods on the Heat of Chemical Combination. 47 



from the hands of the Creator. I do not speak theologically ; 

 but, philosophically considered, the molecular constitution of 

 matter proves that the present arrangement of things must have 

 existed since their formation. 



(20.) I do not think then that it is necessary to suppose an 

 attraction exists between the particles of bodies to account for 

 their coherence ; and as to repulsion, to account for the dilata- 

 tion of a gas when pressure is removed, I think it not only un- 

 necessaiy, but inconsistent when applied to different cases. For 

 instance, it is generally imagined repulsion is the only force 

 operating in gaseous bodies, whether this repulsion is attributed 

 to that force existing in the particles of matter themselves in the 

 state of gas, or resulting from the repulsive power of the sup- 

 posed subtle fluid, heat. ^Tien, however, a cold body is placed 

 in contact with steam, the steam is condensed into water. How 

 could such a change take place according to the usually received 

 theory ? Suppose even that the cold body abstracted the heat, 

 what is to bring the particles of steam together ? There is no 

 attraction ; in fact there is nothing to account for it. If, how- 

 ever, we attend to the circumstance, that as much expansion as 

 is lost by the steam is taken up by the iron, that is, relatively to 

 the space they occupy, we can at once see that at the temperature 

 attained by the two bodies when in contact, each possesses a de- 

 finite bulk, and that the one supplies the opposite movement to 

 enable the other to gain this certain volume. But the subject 

 of attractions and repulsions is admittedly full of inconsistencies ; 

 the theory, or rather the observed facts which I bring forward, show 

 they are not necessary. I offer no theory to account for 

 the cause of contraction and expansion requiring to be accom- 

 panied by each other, or why they are present in different bodies. 

 It is a final cause, and as such, I believe, can never be explained ; 

 and the less we add hypothetical fluids and forces to the pheno- 

 mena we witness, the better I believe we shall understand what 

 takes place. I will just mention, that in the Supplementary 

 Number of this Journal for June last, a paper from Mr. Rankine 

 shows that " the compressibility of water varies according to the 

 same law with that of a gas ;" and this affords, when properly 

 considered, a reason that we should not attribute repulsion to 

 the particles of a gas, if not to water. 



(20*.) If pressure be removed from a gas, it expands for the 

 same reason that a cold body expands in the vicinity of a hot 

 one, viz. to attain the relation that must exist between its volume 

 and that of surrounding bodies; and as the hot body contracts 

 in proportion to the expansion of the cold one, so do the sur- 

 round. ng bodies contract in proportion to the expansion of the 

 gas. When the two bodies are solid, the contraction of the hot 



