Notices respecting New Books. 149 



■ *' All tbe different substances in nature, nnder certair» 

 circumstances, are probably capable of assuming all these 

 forms : thus solids, by a certain increase of temperature, 

 become fluids, and fluids gases ; and vice versa, bv a di- 

 minution of temperature gases become fluids, and fluids 

 Solids." 



" As attempts have been made tu account for attraction, 

 by the supposition of the existence of a peculiar matter, so 

 calnrific repulsion has been accounted for bv supposing a 

 subtile fluid, capable of combining with bodies, and of se- 

 parating their parts from each other, which has been named 

 the nwtter of heat, or enteric. 



" Many of the phjenomena admit of a happy explana- 

 tion on this idea, such as the cold produced during the 

 conversion of solids into fluids or gases, and the increase 

 of temperature connected with the condensation of gases 

 and fluids 5 but there are other facts which are not so easily 

 reconciled to the opinion : such are the production of heat 

 by friction and ) ercussion ; and some of the chemical 

 changes which have been just referred to. When the tem- 

 perature of bodies is raised by friction, there seems (o be 

 no diminution of their capacities, using the word in its 

 common sense: and in many chemical changes connected 

 with an increase cf temperature, there appears to be like- 

 wise an increase of capacity. A piece of i'on made red 

 hot by hannnering cannot be strongly heated a second time 

 by the same means, imless it has been previously intro- 

 duced into a fire. This fact has been explained by sup- 

 posing that the fluid of heat has been pressed out of it, by 

 the percussion, which is recovered in the fire : but this is a 

 very rude mechanical idea : the arrangements of its parts 

 are altered by hannnering in this way, anci it is rendered 

 brittle. By a moderate degree of friction, as it would ap- 

 pear from Runiford's experiments, the same liece of metal 

 may be kepi hot for any Icniith of time; so that, if heat 

 be pressed out, the quantilv must be inexhaustible. When 

 any body is cooled it occupies a smaller volume than be- 

 fore: it is evident, therefore, that its parts must have ap- 

 proached towards each other: when the body is expanded 

 by heat, it is equally evident ihat its parts must have se- 

 parated froju each other. The immediate cause of the 

 phaenomena of heat, fheuj is motion, and the laws of its 

 communication are precisely the same as the laws of the 

 coinmunicaiion of motion. 



" Since all matter may be made to fill a smaller volunie 



by cooling, it is evident thai the panicles of matter- must 



K 3 have 



