/. LeConte on the Injluence of Sola?- Light on Combustion. 325 



be in tlie ratio of \^1500-80 : VloOO-60 =^^1420": VfllO 

 1 : 1'0070. When, how^ever, the comparison is made between 



summer 



cause will be more sensible, and ought not to be entirely over- 

 looked.* 



On the contrary, it \^ possible^ that an augmentation of temper- 

 ature might tend to accelerate the process of combustioDj bj 

 favoring the liquefaction of the wax, and, perhaps, facilitating 

 the oxydation of the combustible matter. If any such influence 

 is exercised, it is probable, however, that its effect must be inap- 

 preciable under ordinaiy circumstances. Under this view of the 

 subject, the only obvious influence which atmospheric heat exer- 

 cises on the rapidity of combustion, is connected with its effects 

 on the density of the air: and that, consequently, an increase of 



temperature should, cceteris paribics^ retora combustion, emd vice 

 versa, 



3. Amount of Aqueous Vapor jpresenf. 



Sir Humphry Davy found that "a very large quantity" of 

 5fea??i was required to prevent sulphur from burning; that an 

 explosive mixture of oxygen and hydrogen, when mixed with 5 

 times its volume ofsteam^ still exploded by the electric spark ; and 

 that a mixture of air and carburettcd hydrogen gas, required ''a 

 tfiird of steam to prevent its explosion, whereas ]■ of azote pro- 

 duced the effect-"! Under any point of view, it is obvious, that 

 the presence of aqueous vapor can only tend to retard the pro- 

 cess of combustion. First^ because it diminishes the amount of 

 oxygen in a given volume of air, and secondly, because an ad- 

 53iixture of any inactive gas tends to extinguish the burning 

 ^ody, as is abundantly proved by the experiments of Sir II. 

 I^avy and others. When vapor is present in large quantities, 

 there can be no doubt of its controlling agency on combustion. 

 This is illustrated by the successful application of the plan pro- 

 posed by M. Dujardin of Lille, in 1837, for extinguishing fires 

 occurring in steam-ships, by pennitting the steam from the boilers 

 to escape into the apartment in which the combustion originates.^ 

 But experiments are still wanting, for determining its influence 

 on tlic rate of burning, when existing in the small quantities in 

 ^hich it is usually associated with the atmosphere.§ The exper- 



* I endeavored to test the influence of temperature on the rate of comhustioD, by 

 placing the burning candle over a large heated plate; but,— as might have been ex- 

 pected,-~the icnsteadiness of the fame renderecl the experiment unsatisfactoiy. 



t Phil. Trans, for 1817, p. 65. 

 A Comptes ReuJus, Tome 5, p. 28. Paris, 183Y: also, Tome 35, p. 368, et 706, 



Paris, 1852. 



§ The curious results obtained by Mr. J- F. Dana, and subsequently Mr. Samuel 

 Morey, in relation to increasing the brightness of the flames of highly carbonaceoua 

 combustible^ by throwing a jet of steam into them, are obviously inapplicable to 

 candles, (^ide, SiUiman's Journal, 1st Series, vol. 1, p. 401; toL 2, p. 118, 122 ; 

 and vol 1, p. 143.) 



