1208 0N THE THEORY OF COMBUSTION. 



Now as the ultimate change produced on combuftibles by 



both thefe fets of bodies is the fame, and as the fubftance 



which combines with the combuftible is the fame, namely oxi- 



gen, it is evident, that the oxigen of the fupporters contains 



fomething, which the oxigen of the produces wants," and this 



fomething the Do&or fuppofes to be caloric. " In the fame 



manner the combuftibles and products referable each other, the 



chief difference between them conn* fling, in the phenomena 



which accompany their combination with oxigen, in the one 



cafe fire is emitted, and in the other not." Now fays the 



Doctor, " if we recollect, that no fubftance but a combuftible 



is capable of reftoring combuftion to the bafe of a product, 



and that at the time of its doing fo, it always lofes its own 



combuftibility, and further, that the bafe of a product does not 



exhibit the phenomena of combuftion even when it combines 



with oxigen, we cannot avoid concluding that all combuftibles 



contain an ingredient, which they lofe when converted into 



products, and that this lofs contributes to the fire, which 



makes its appearance during the converfion." This ingre- 



Leading pofitfons dient the Doctor fuppofes to be light. It is evident, that the 



i! thltligh^'s tvvo leadi "g pofitions of this theory are, 1 . That during com- 



originally an in- buftion, all combuftibles emit light, which previoufly formed 



buftbl 11 ° f C ° m " a ncce ^ r J ingredient to their own compofition ; and fecondly, 



and heat of oxi- That the heat which is evolved during the procefs of combuf- 



£ en « tion, proceeds from the oxigen of the fupporter, of which it 



Many reafons likewife originally formed an efTential ingredient.— That the 



muVco hC f C ^ eat g* ven out during combuftion comes from the decompofi- 



the oxigen of the ti° n of the oxigen of the fupporter, there are many reafons for 



fupporter. concluding. We know very well that no combuftion will take 



place without the prefence of oxigen, and that the greater the 



quantity of oxigen abforbed in a given time, the greater is 



always the heat that is evolved. Now if the heat be not fup- 



pofed to come from the oxigen, why fhould the degree of heat 



given out, be always proportional to the quantity of oxigen 



that is abforbed, and upon what other principle can we fo 



fatisfactorily explain the effects that are produced by the Argand 



lamp. Thefe confiderations, combined with the argument 



drawn from the maintenance of the temperature of hot blooded 



animals by the decompofition of air, feem fuffieiently to efta- 



Difficultics as to blifh the truth of the foregoing pofition. There arc, however, 



t!on 0t th r P tl fl ~ man ^ difficulties tnat P re ^ s a gainft our implicit adoption, of the 



light invariably Other 



