152 T. S. Hunt—Celestial Chemistry. 
or no this medium is (as appears to me most probable) a con-. 
tinuation of our own atmosphere, its existence cannot be ques- 
tioned.” He then attempts to fix an inferior limit to the den- 
the thermal unit. He concludes “that the luminiferous me- 
dium is enormously denser than the continuation of the terres- 
trial atmosphere would be in interplantary space if rarified ac- 
cording to Boyle’s law always, and if the earth were at rest in 
a state of constant temperature, with an atmosphere of the act- 
ual density at its’surface,” The earth itself in moving through 
space ‘cannot displace less than 250 ounds of matter.” 
In 1870, W. Mattieu Williams published his very ingenious 
work entitled The Fuel of the Sun, in which, apparently with- 
out any knowledge of what had been written before with regard 
to an interstellary medium, he attempts to find therein the 
source of solar heat—the “solary fuel” of Newton. To quote 
his own language, “the gaseous ocean in which we are im- 
t. p. 5). 
Since the days of Newton, however, no one had hitherto con- 
sidered the interstellary matter from a chemical. point of view. 
conception of Humboldt that its condensation gives rise to 
nebula, ventured the suggestion that from an etherial medium 
accordance with the views of Brodie, Clarke, and Lockyer, by a 
stoichiogenic process; so that in the language of Newton’s Hy- 
; ? 
pothesis, ‘ 
It was not, however, until 1878, that, from a consideration of 
the chemical processes which have gone on at the earth’s sur- 
face within recorded geological time, I was led to another step 
in this inquiry. ‘That all the de-oxidized carbon found in the 
earth’s crust in the forms of coal and graphite, as well as that 
existing in a diffused state, as bituminous or carbonaceous mat- 
ter, has come, through vegetation, from pheric carbonic acid, 
appears certain. To the same source we must ascribe the carbone 
acid of all the limestones which, since the dawn of life on ou 
earth, have been deposited from its waters. It is through the 
sub-aérial decay of crystalline silicated rocks, and the direct 
formation of carbonate of lime, or of carbonates of magnesia 
and alkalies which have reacted on the calcium-salts of the pri- 
