Our Atmosphere and the Ether of Space. 213 



oxygen is gently issuing. The flame will appear to attach itself to 

 the oxygen tube., and the jet of oxygen will be burning in an 

 atmosphere of hydrogen. Combustion in fact occurs at the 

 place where the two gases first came into contact. Suppose 

 for a moment that the earth's atmosphere had contained 

 hydrogen instead of oxygen ; oxygen would have appeared to 

 us in the light of a combustible gas ; hydrogen in that of a 

 supporter of combustion." 



The term ' ' more igneous " may not be intelligible without 

 considering the sense in which Sir John Herschel employed it, 

 in the letter to M. Quetelet, from which M. Hansteen adopted 

 it. Sir John said, that the great elevation of shooting stars above 

 the earth " leads to the conjecture of an upper aerial atmosphere, 

 lighter and so to say more igneous." Mr. Alexander Herschel 

 has provided us with some remarks on this subject. He observes, 

 "that according to the calculations of Thompson and Joule a body 

 moving with a velocity of thirty-nine miles per second will 

 heat the air, of whatever density, in immediate contact with 

 it, two million degrees. Surely such velocities are more 

 likely to exist in the highest and thinnest strata of the 

 atmosphere, than in the lower denser parts, where storms and 

 clouds, etc., are prepared, and in this sense the upper atmos- 

 phere may be called the igneous atmosphere, because it is more 

 exposed to such igneous catastrophes from which the lower 

 strata is happily defended." 



If we consider the effects of heat and pressure in modify- 

 ing the condition of matter, it will appear probable that 

 there are limits to the existence of compounds having definite 

 properties, both in a pressure range and a temperature range 

 — that is to say, that no compound could be heated, or cooled, 

 beyond a certain point without its becoming decomposed, or 

 having its particles re-arranged into a new substance. And 

 also that no compound could be condensed, or rarified, beyond 

 certain limits without undergoing decomposition or change. 



The grounds for conceiving the earth's atmosphere to be 

 only forty or fifty miles high were incomplete. It was supposed 

 that at about that distance from the earth the elasticity of the 

 air and the force of gravity balanced each other. M. Quetelet 

 now shows reason for believing that an upper atmosphere 

 exists, and he assigns to it a different composition. May it 

 not result from a resolution of the earth's lower atmosphere 

 into some other form of matter? Oxygen and nitrogen may 

 be compound bodies, and may be decomposed under such 

 remarkable conditions of temperature, pressure, etc. Even if 

 we regard them as simple substances, we have no right to limit 

 their capacity for existing under different conditions, and with 

 very different properties. The difficulty of defining a species 



