1820.] Mathematical Principles of Chemical Philosophy/. 351 



AUTICLE IV. 



Researches into the Mathematical Principles of Chemical Philo- 

 sophy. By J. B. Euimett. (With a Plate.) 



{Continued from p. 188.) 

 SIR, Hull, Sept. 6, 1820. 



Caloric appears to be an elastic fluid, of very great rarity,, 

 and possessing an eminent degree of elastic force ; capable of 

 condensation and rarefaction, attracted by every form of ponder- 

 able matter, but its own particles seem to be mutually repellent. 

 That it is an elastic fluid appears highly probable from the phe- 

 nomena of its absorption and emission ; a given mass of one form 

 of matter, in passing from any one to any other degree of tem- 

 perature, will absorb or emit more heat than an equal mass of 

 another ; if, therefore, it be admitted to be a material agent, it 

 must be susceptible of condensation and rarefaction, which may 

 also be proved from the fact of the existence of various degrees 

 of heat. That it is elastic appears evident from the ft\cility with 

 which it is reflected by polished surfaces, the angle of incidence 

 being equal to the angle of reflection ; this property is also ren- 

 dered highly probable from the circumstance of its communicat- 

 ing an eminent degree of elastic force to those particles of 

 ponderable matter with which it is combined. That it is 

 attracted by ponderable matter is demonstrated by numerous 

 experiments ; Avhen a mass of matter is heated above the temper- 

 ature of the surrounding medium, the sensation of heat is 

 perceived at a very considerable distance, and is the most intense 

 at the nearest distances from the surface. Now since heat 

 always endeavours to dilate itself into indefinite space, the phe- 

 nomena are perfectly inexplicable, except we admit that that 

 which produces the sensation of heat is attracted by the mass of 

 ponderable matter. Since a full proof of this property of caloric 

 is of primary importance, it may not be improper to dwell a little 

 longer upon this subject, and confirm the statement by a variety 

 of proper experiments. Let an ignited conical point of chai'coal 

 be held over a piece of ice, or other cold substance, the redness 

 of the extremity will disappear when there is a very perceptible 

 distance between it and the colder matter, and be renewed 

 when it is withdrawn. If a small thermometer be used instead 

 of the ice, it wiU indicate an elevated temperature ; but if a 

 heated mass of matter be employed, no sensible eflect results; 

 since in these experiments there can be no current of air esta- 

 blished, by which the heat can be removed, there remains only 

 an attracting force, by which the eflect can be produced: besides 

 the mere circumstance of heat attaching itself to solid matter, 

 or to ponderable matter generally, is sutticient to prove that an 

 attracting force is operative between them. Numerous cases of 



