NATURAL PHILOSOPHY. 1G1 



drogen the temperature is higher than in any other gas. 3. In this 

 gas the temperature is higher than in vacua ; and the denser the gas 

 is, the higher is the temperature. 4. Hence, hydrogen conducts heat 

 like metals. 5. In all other gases the temperature is lower than in 

 vacua ; and the denser they are, the lower is the temperature. 6. It 

 cannot hence be concluded that gases do not conduct heat, but only 

 that they do this in so small a degree that the action of conduction is 

 cancelled by their diathermancy. 7. This remarkable property of 

 hydrogen is evinced not only when it moves freely, but also when it is 

 contained between eider down, or any loose substance which hinders 

 its motion. 8. The great conductibility of this gas is a further con- 

 firmation of its analogy with metals. 9. Hydrogen conducts not only 

 heat, but also electricity, better than other gases. 



COMBUSTION IX EAEIFIED AIR. 



Dr. E. Frankland, in a recent paper on the above subject before 

 the Royal Institution, stated that in the autumn of 1859 he burnt 

 candles protected from draught on the summit of Mont Blanc and at 

 Chamounix, with the view of determining the effect of various degrees 

 of atmospheric pressure on the amount of combustible matter con- 

 sumed. He found, as the average of five experiments, that a stearine 

 candle diminished in weight 9. 4 "grammes, when burned for one hour 

 at Chamounix, and 9.2 grammes when ignited for the same length of 

 time upon Mont Blanc. These experiments went to prove that the 

 ratio of combustion was almost independent of the density of the at- 

 mosphere, as the pressure at the two places varied several inches in 

 the barometer. But when burning the candle on the top of the 

 mountain it was noticed that the flame was not so brilliant as in a 

 more dense atmosphere. These results induced him on his return to 

 England to make experiments with a coal-gas flame burning in a glass 

 jar under different pressures of the atmosphere, produced by artificial 

 arrangements. He passed the gas through a governor valve, secured 

 a uniform flow in the burner, and the experimental flame was placed 

 at one extremity of a Bunsen's photometer. Near this flame was 

 placed a similar jet surrounded with a glass shade, but it was permit- 

 ted to burn freely in the air so as to compare it with the other flame 

 that was subject to variations of atmospheric pressure. From data 

 gained in this way, Prof. Frankland was led to the conclusion that 

 the rarefaction of air, from atmospheric pressure downwards, produces 

 a uniformly diminishing illuminating power until the pressure is re- 

 duced to about 14 ins. of mercury, below which the diminution of light 

 proceeds at a less rapid rate. Thus, an amount of gas which would 

 give a light equal to 100 candles when the barometer stands at 31 ins., 

 would give a light equal to only 84.4 candles if the barometer fell to 

 28 ins. The question, however, which Professor Frankland found the 

 most difficulty in solving was, the decrease of luminosity of the flame 

 with the decreased pressure of air, while the combustion of the gas 

 was about the same in quantity in both cases. His final conclusion was 

 that this anomaly was due to the circumstance of a greater quantity 

 of air finding access to the interior of the flame. 

 H* 



