52 CORRELATION OF PHYSICAL FORCES. 



attraction of cohesion or aggregation, yet both gases and solids 

 expand or contract according to the inverse contraction or 

 expansion of other neighbouring bodies, and so far resemble 

 each other in their relations to heat and cold. The extent to 

 which such expansion or contraction can be carried, seems to 

 be limited only by the correlative state of other bodies ; these, 

 again, by others, and so on, as far as we may judge, throughout 

 the universe. 



Adopting the explanation above given of the decomposition 

 of water by heat, heat would have the same relation to che- 

 mical affinity as it has to physical attraction ; its immediate 

 tendency is antagonistic to both, and it is only by a secondary 

 action that chemical affinity is apparently promoted by heat. 

 This hypothesis would account for heat promoting changes of 

 the equilibrium of chemical affinity among mixed compound 

 substances, by decomposing certain compounds and separating 

 elementary constituents whose affinity is greater, when they 

 are brought within the sphere of attraction for the substance 

 with which they are mixed, than for those with which they 

 were originally chemically united : thus an intense heat being 

 applied to a mixture of chlorine and the vapour of water, 

 occasions the production of muriatic acid, liberating oxygen. 



Carrying out this view, it would appear that a sufficient 

 intensity of heat might yield indefinite powers of decomposi- 

 tion ; and there seems some probability of bodies now supposed 

 to be elementary, being decomposed or resolved into further 

 elements by the application of heat of sufficient intensity ; or, 

 reasoning conversely, it may fairly be anticipated that bodies, 

 which will not enter into combination at a certain temperature, 

 will enter into combination if their temperature be lowered, 

 and that thus new compounds may be formed by a proper 

 disposition of their constituents when exposed to an extremely 

 low temperature, and the more so if compression be also 

 employed. 



The term 'dissociation' has been applied by M. St. Clair 

 Deville to my experiment of the separation of oxygen and 

 hydrogen by heat, and to other cases, in which heat separates 

 the constituents of a substance without any of them combining 

 with another body, thus contradistinguishing these effects from 



