NATURAL PHILOSOPHY. 203 



there can be no doubt of its controlling agency on combustion. This is il- 

 lustrated by tlie successful application of the plan proposed by M. Dujarclin 

 of Lille, in 1837, for extinguishing fires occurring in steam-ships, by per- 

 mitting 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 the rate of burning, when existing in the small quantities in 

 which it is usually associated with the atmosphere. The experimental re- 

 searches of Mr. David Waldie, in relation to the mixture of various gases 

 with air, led him to the general law, that, " Of incombustible gases which re- 

 main undecomposed, the power of preventing combustion is in the order of 

 their density ; " and that, " This effect of density in cooling the flame de- 

 pends on the excessive diffusion of the flame in the denser gas." Under or- 

 dinary circumstances, the density of the aqueous vapor existing in the air is 

 comparatively small, so that, according to Mr. Waklie's law, its influence 

 on combustion ought not to be very striking. 



Having illustrated the influence of these three external conditions, Pro- 

 fessor Le Conte next proceeded to investigate whether these were adequate 

 to explain the variations in the rates of burning as indicated by observation. 

 The observations requisite for testing the effects of aqueous vapor were 

 wanting ; but the effects of barometric pressure and temperature, were sub- 

 jected to a quantitative test, on the assumption that the rapidity of combus- 

 tion varies directly as the density of the air. By the application of a ma- 

 thematical formula, he was enabled to apply this test to his own experi- 

 ments." The ratios between the rates of combustion, were thus compared 

 with the ratios between the corresponding densities of the air under different 

 circumstances. The general result of this comparison was, that the varia- 

 tions in the density of the air are not adequate to explain the whole of the 

 differences in the rates of burning ; they explain the greater part of these 

 differences, but there is a small per ccntage of excess in the rates of combus- 

 tion, which he thinks attributable to the influence of aqueous vapor, and per- 

 haps other causes not yet considered. 



In the present stage of the investigation, Professor Le Conte thinks that 

 two deductions ai-e wan-anted. 1. That solar light does not seem to exercise 

 any sensible influence on the process of combustion. 2. That variation in 

 the density of the air does exercise a very decided influence on the rapidity 

 of the process : the rate of burning increasing with every increment of den- 

 sity, and vice versa : but the exact ratio between them remains to be de- 

 termined. 



ON THE XATUHE OF HEAT. 



At the recent meeting of the German Association for the Promotion of 

 Science, Baron Bauingartner discussed the alteration of some fundamental 

 ideas concerning the nature of heat, which would probably take place in con- 

 sequence of recent researches. About half a century ago, every series of sim- 

 ilar phenomena was explained by the hypothesis of a special imponderable 

 fluid. The undulatory theory of light led the way in the opposition to this 

 materialistic tendenc^y, and the development of the undulatoiy theory offers 



