1.50 X On Elasticity. 



viz. that of the metallic rnolccuhs for the newly interposed 

 body ; for, could that new affinity be destroyed, or, in other 

 wordj!, could the interposed substance be entirely removed, 

 it is probable the aBinity of the inoleculoe would again be 

 exerted. Of this some idea mav be formed by attending to 

 what takes place when two spheres of lead, a little ilattened, 

 are pressed together. In piopcrtion as the air has been ex- 

 cluded will be the adherence of the two balls. 



We would not wish, however, to be understood to assert 

 that in every case a disjoined mass would unite but for the 

 newly interposed substance, for several conditions are re- 

 quisite to this eflect which can rarely exist. Among these 

 may be mentioned, that there should be no new arrange- 

 ment of portions of the broken surfaces by the metal having 

 by its tenacity drawn itself out into fibrous [iganients and 

 protrusions ; for in that case the points of contact upon 

 joining the masses are so limited that the very weight of 

 either part, that is_, its gravity for the common centre of 

 attraction, will act as a sufficient force to destroy the affinity 

 which exerts itself to keep them united. We may also here 

 remark, that in the confused crystallization of melted masses 

 of metal, some of the portions may always be conceived to 

 be under some restraint, as it were, and this must hold also 

 after the metal has been hammered. Therefore on breaking 

 the mass some of these will always protrude, or in some 

 way or other change their position a little, so as to produce 

 an effect similar to that before described — reducing to a 

 comparatively small number the points that can be brought 

 into contact. Therefore v.'hat we mean to suggest is only 

 this — that if every interposed substance couid be entirely 

 removed, and it were possible to bring the original number 

 of points into contact, the affinity of aggvegatioii would act 

 to unite the parts of the mass. 



I might apply the reasoning employed in the case of the 

 spring AB to other cases of soHd bodies; but, from what I 

 have said, I think any person may apply my reasoning in 

 the same way as I would myself, whether he be convinced 

 of its truth or not ; to enlarge further appears therefore un- 

 necessary. It is proper, hov.ever, that I shotdd endeavour 

 to show how the same doctrine applies to aeriform fluids. 



When air is compressed, on removing the force it regains 

 its first volume. This, however, is conditional. If the 

 compressed air be of a given temperature, say 80°, and if 

 it be afterwards reduced to a lower temperature, say .t2°, it 

 may so happen that the diminution of volume by reduction 

 of tcniperature may more than counterbalance the com- 



prcssingj 



