212 Our Atmosphere and the Ether of Space. 



height of this meteor as seen from neighbouring places, and 

 using the telegraph as an aid." 



Cosmos also gives a letter from M. Hansteen of Christiana, 

 to M. Quetelet, in which he says : — " Your last article on 

 shooting stars and their place of appearance, has particularly- 

 interested me, on account of the idea put forth, by you and 

 approved by Sir John Herschel, H. A. Newton, and Aug. 

 de la Rive, that beyond the lower atmosphere in which we 

 live — and which you call the unstable atmosphere — there 

 exists a second atmosphere three times as high— and which you 

 term the stable atmosphere — of different composition, much 

 lighter, and therefore, so to say, more igneous. It is only in 

 this latter atmosphere that auroras manifest their luminosity. 

 The upper atmosphere in which auroras and shooting stars 

 appear as luminous bodies, may be nothing else than a very' 

 rarified hydrogen, very light and very inflammable. The 

 period of revolution of Encke's comet, which diminishes one- 

 tenth of a day at each revolution, suggests the existence of a 

 resisting medium, which is accounted for by supposing the 

 presence of a certain ether, the nature of which is unknown. 

 May not this ether be very rarified hydrogen diffused through 

 space." 



The suggestions of M. Hansteen, though interesting, are 

 open to certain objections. Why does he imagine the upper 

 atmosphere to consist of hydrogen ? Is it simply because that 

 is the lightest body we are acquainted with on the surface of 

 our globe ? There is no reason whatever to suppose th,at the 

 lightest body we know must resemble in composition, or be 

 identical with, any lighter body that may exist somewhere else 

 under totally different conditions. Nor is there any- reason for 

 supposing that the inflammability of hydrogen would be aug- 

 mented by enormous rarefaction. 



When a body is called inflammable we should remember 

 that the term is not very precise. 



It is customary to speak of certain bodies as being either 

 combustible, or supporters of combustion ; but the following 

 remarks of Professor Miller placo this subject in a clear light 

 and show how easily tho terms become convertible. He 

 tells us* that " a striking experiment may bo performed with 

 hydrogen, which shows how purely conventional are tho terms 

 ' combustible' and ' supporters of combustion .' Let a tall bottle 

 with a narrow neck be filled with hydrogen gas; through a 

 cork which pusses easily into the neck of tho bottle, fit a jet 

 connected with a gas-holder containing oxygen ; place the 

 bottle mouth downwards and set fire to the hydrogen, then 

 immediately insert tho cork and jet through which a stream of 

 * Elements of Chemistry^ Part II. p. 48. Second edition. 



