176 Analysis of Scientific Books. 
change in these lofty regions, and pass into a sort of ethereal 
essence, more analogous to diffuse light than to a mass of air.” 
Or in other words, perhaps the air ceases to be air, and then 
its elevation can exceed a certain limit, contrary to his own pro- 
position. 
In treating of the constitution of the atmosphere, he says, it 
may be doubted whether the chemical analysis be complete, 
adding, “‘ The combination of these gases (oxygen, azote, and 
carbonie acid,) obtained artificially, generates a fluid, in which 
wecan hardly recognise the ordinaty qualities of atmospheric 
air. Some fugacious elements must therefore escape, during 
the process of decomposition.” We know not on what chemi- 
cal authority Mr. Leslie makes this assertion, nor are we aware 
of any chemist having shewn that pure azote, oxygen, and car- 
bonic acid, in due proportions, form a mixture, ‘‘ in which we 
can hardly recognise the ordinary qualities of atmospheric air.” 
On the contrary, this mixture certainly possesses all the ordi- 
nary relations to animal life, combustion, and humidity, which 
native air does. 
The following speculations appear altogether fanciful :— 
Buta variety of circumstances render it extremely probable, that an ex- 
panse far above the region of the clouds, is filled by some peculiar fluid, 
very different from the grosser element spread below. The shooting stars, 
which are seen every clear night, the bolades, or fire-balls, and the luminous 
arches which not unfrequently occur, and which must traverse the sky at 
the height of several hundred miles, all seem to indicate the existence of a 
very ignitible medium. — Nor is it difficult to conceive how such a collec- 
tion ofhighly inflammable fluids could be formed. Not to mention the 
multiplied processes of art which emit those products, the great laboratory 
of nature is incessantly at work in generating and pouring forth hydrogen 
gas, and its various compounds. The volcanic mountains ever a con- 
siderable portion of the surface of the globe, and their innumerable 
spiracles, with scarcely any interruption, continue to discharge immense 
streams of inflammable aérial fluids, a great part of which escape confla- 
gration. Butas hydrogen gas has little attraction to common air, it rises 
upwards by its buoyancy, without suffering much loss in its passage 
through that fluid. The largeness of their volume, and the celerity of 
their projection, conspire to favour the ascent of those inflammable gases 
to the Joftiest regions of the atmosphere. A comparison of the several 
quantities of astronomical refraction at different altitudes, points to a 
similar conclusion. The refraction which the rays of light suffer in slanting 
across the higher regions of the air, is greater than what calculation assigns 
to the corresponding density of the medium. But the discrepancy would 
entirely disappear, if we suppose these strata to consist of hydrogen gas, 
which is known to possess, in a remarkable degree, the power of refrac- 
ting*. 
Mr. Leslie forgets that a collection of highly inflammable 
fluids cannot be inflamed, unless in intimate contact with 
some different kind of fluid, with which they may combine. As 
to the argument. from astronomical refraction, we shall not put 
* Pi 828. 
