ok THE THEORY OF COMBUST ION". '211 



Which mould take place according to the Doctor's theory; 

 water, which is a product of cbmbuftion, is hidrogen without Numerically 

 its light, in union with oxigen, without its heat ; by adding ™" ^fitton of 

 iron (a combuftible containing light) we decompofe the water, precifely ade- 

 that is to fay, 73 parts of iron unite with 27 of oxigen. Now jK C {^^f 

 as to every 27 parts of oxigen in water there are about four buftible to com- 

 ofhidrogen, ofcourfe thefe four parts of hidrogen are libe- buftible, &c 

 rated ; but as it does not appear probable that combuftibles 

 fliould be capable of combining with light in all proportions, 

 it may be aiked> if the 73 parts of iron which are oxidated 

 contain juft light enough, and no more, to reftore the com- 

 buftibility of the four parts of hidrogen ; for if there be too 

 much for that purpofe, the fuperabundant quantity ought td 

 become vifible, and if too little, a part only of the hidrogen 

 fhould recover its combuitibility, and be converted into gas. 

 And the fame reafoning may of courfe be urged with regard 

 to the deeompofition of water by zinc : for it cannot but be 

 acknowledged, that the fact is fomewhat fingular, that the 

 product of combuftion mould always contain and give out the 

 precife quantity of light which is fufficient to reftore combuf- 

 tibility to the bafe of the product, and in no cafe either more 

 or lefs. Thus it appears that there are many difficulties that Conclufion. 

 attend our implicit affent fo the prefent theory, and many of 

 the phenomena of combuftion that do not apparently admit 

 from it of an eafy interpretation. Whether Dr Thomfoh can 

 reconcile thefe apparent anomalies to it, remains to be feen 5 

 but if it is found equal to their folution, there, could then it 

 fhould feem be little objection to its adoption. At all events, Dr.T. has 

 ho one will be inclined to difpute, that the Doctor has *™ wn S r * at > 

 thrown much light on a fubject> which before its inveftigation f cure fubjeft, 

 by him, was considerably more obfcure: and that he has 

 placed it in a new point of view, which bids fair to enable us 

 to approximate much nearer to a true theory with regard to 

 the phenomena of combuftion, than any other that has hi- 

 therto prevailed. 



G. P.- 



tf£ XV, On 



