*>Q$ *K THE MATERIALITY OF CALORIC. 



Mechanical A circumftance, . abfolutely eflential to the formation of 



preffure prevents f ; thafc ffee f ^ be a j| owed f 0r the j r expaivfion. 



the formation of ° , ' . „ r rt r V,. 



gasj but is not Mechanical preflure acts as a counteracting torce to this ex- 



an argument panfion : -and either prevents it completely, or pnrtia'rly, 4c- 

 againil this doc- ^ ' ' r _. .. "J '' ' / 



vine# cording to the degree or, its application. But from this fact, 



no argument can be drawn againft the exiftence of chemical 

 affinity, as an attribute of caloric. Two oppofite forces in 

 phyfics raay be fo balanced,- that neither fliall produce it's ap- 

 propriate effect. Thus* 'a body, impelled in contrary direc- 

 tions, may remain at reft, yet the operation of the oppofing 

 forces, in this cafe, cannot be denied. Even in ' chemiftryy 

 we have unequivocal examples, in which the adion of the 

 affinities is fupprefied by more ■powerful eaufes. Thus bodies, 

 that have a ftrong chemical affinity, atfe kept perfectly diftinct, 

 even when placed in contact, by the affinity of aggregation; 

 The only inference, then, that can fairly be adduced from 

 the effects of preffure-, ■ in preventing the formation of gafes, is, 

 that it is a power, fometimes fuperior,* in energy, to that of 

 chemical affinity. 

 Caloric having Since, therefore, caloric is characterized by all the proper- 



all the proper- tj excC pt gravity, that enter into the definition of matter- 

 ties of matter, ' r & J » 



but gravity may we may venture to confider it as a diftinct and peculiar body, 



be taken to be ^ or j s j ts deficiency of gravity fufficient to exclude it from 



the clafs of material fubft ances*. Such nicety of arrangement 



might, with equal propriety, lead us to deny the materiality 



of light, the gravity of which has never yet been proved : for* 



befides the experiments of Mr. Michelf which failed in afcer- 



tainingthis property of light, we have feveral chemical fact* 



tending to the fame conclafion. ' Thus Mr.' Cavendith, after* 



firing a mixture of hidrogenousand oxigenous gafes, in a'clofc* 



x veflfel, a procefs during which much light is always emitted,- 



found not the finalleft diminution of weight. 



Phenomena cf To have completed this defence of the material nature of 



heat differ heat ^ j t would have been proper to have pointed out the c -ir- 



Hiotion. cumftances, in which the phenomena of heat differ from the 



known and acknowledged phenomena of motion. At prefent, 



however, I have not leifure to purfue the fubject at much 



length ; and, though feveral points of difagreement woulcf 



doubtiefs be found, I (hall mention only one of the nioft 



marked and decifive. 



Motion 



