1874.] J-"^ [Marsh. 



degrees (about the temperature of melting lead) ; whilst at the height of 

 seventeen miles, the whole of the latent heat would be required to raise 

 the temperature of the air only twenty degrees. From this it is evident 

 that "latent heat " fails entirely as a source of luminosity at all heights 

 below forty miles. On the other hand, whilst at great heights the effect 

 of "resistance" is insignificant and altogether inadequate to the pro- 

 duction of any splendor, its power at the height of forty, or even of fifty 

 miles, seems almost unlimited. "Latent heat" and "resistance" to- 

 gether cover the whole field. Luminosity from "resistance" would 

 commence at a height of eighty-five miles, more or less, according to 

 velocity, and would increase rapidly with decrease of height, so that at 

 the height of thirty-four miles it would be more than thirty thousand 

 times as great as at eighty-five miles ; whilst "latent heat" would cause 

 the meteor to burst out in full splendor as soon as it had penetrated the 

 atmosphere far enough to develop an amount of heat competent to vapor- 

 ize its outer layer : and to disappear entirely, at a height of more than 

 forty miles. 



It is a significant fact, that very few meteors have been known to re- 

 tain their luminosity below that point. Indeed, whilst some of the 

 observed phenomena are such that "resistance" alone cannot afford any 

 explanation whatever, they are all in perfect accord with the require- 

 ments of the "latent heat" theory. Hence we seem to be justified in 

 concluding that "latent heat" is the frincipal source of meteoric lu- 

 minosii y. 



The second column in the table gives the heating power of a unit of 

 weight of air at different heights : showing, that one grain at the height 

 of three and a-half miles, if compressed until its density equals that of 

 air at the sea-level, will give out only enough heat to raise the tempera- 

 ture of one grain of air under constant volume about two-thirds of one 

 degree ; but that at the height of eighty-five miles the heat given out will 

 t^uffice to raise the temperature of one grain twenty millions of degrees ; 

 at one hundred and thirty-seven miles, seven hundred thousand millions 

 of degrees ; whilst at the height of two hundred and five miles the 

 number would exceed seven hundred thousand millions of millions. 



This implies a condition of things somewhat similar to that suggested 

 by Mr. Birks in his chapter on the ^^ Igneous condition of matter,'''' - when 

 he says, " There will thus, according to the present theory of the laws of 

 matter, be more truth than has latterly been recognized, in the old 

 arrangement of the four elements, which placed a fourth region of fire, 

 above the solid, liquid, and gaseous constituents of our globe. In fact 

 above the region where the aij, though greatly rarefied, is still elastic, 

 there must be a still higher stratum where elasticity has wholly ceased, 

 and where the particles of matter, being very widely separated, condense 

 around them the largest amount of ether. All sensible heat, in the 



* On Matter and Ether or the Secret Laws of Physical Change, by Thomas Kawson 

 Birks, M. A., Cambridge, (England) 1862. 



