358 T. S. Hunt—Chemical and Geological 
Neither Grove nor Williams has considered the hypothesis 
of an interstellary medium in its geological relations. Dr. P. 
the ey of Grove, has adopted it from Williams,* but in- 
stea 
rinciples already laid down, that these changes have not been 
ue to solar attraction and absorption, but to the chemical and 
mechanical processes going on at the surface of the earth and 
other bodies in space, whereby the atmospheric elements are 
condensed in the forms of liquid and solid water, or fixed as 
hydrates, oxides, carbonates and hydrocarbonaceous matters. 
The changes which have thus been produced in the terres: 
trial atmosphere are, by our hypothesis, reduced in amount b 
being shared with other worlds, and the consequences whic 
* It is due to my friends, Mr. Williams and Dr. Duncan, to say that they have 
both, in conversation, informed me that they were ignorant of the priority of Sir 
William Grove. The conception appears to have been original and independent 
in the mind of Mr. Williams. 
