FRAGMENTS OF SCIENCE. 
CHAPTER I. 
THE CONSTITUTION OF NATURE.* 
WE CANNOT think of space as finite, for wherever 
in imagination we erect a boundary, we are compelled 
to think of space as existing beyond it. Thus by 
the incessant dissolution of limits we arrive at a more 
or less adequate idea of the infinity of space. But though 
compelled to think of space as unbounded, there is no 
mental necessity compelling ns to think of it either as filled 
or empty; whether it is so or not must be decided by ex- 
periment and observatiorf. That it is not entirely void 
the starry heavens declare; but the question still remains, 
are the stars themselves hung in vacuo? Are the vast 
regions which surround them, and across which their light 
is propagated, absolutely empty? A century ago the 
answer to this question, founded on the Newtonian theory, 
would have been, " No, for particles of light are inces- 
santly shot through space." The reply of modern science 
is also negative, but on different grounds. It has the best 
possible reasons for rejecting the idea of luminiferous 
particles; but in support of the conclusion that the celes- 
tial .spaces are occupied by matter, it is able to offer proofs 
almost as cogent as those which can be adduced of the 
existence of an atmosphere round the earth. Men's 
minds, indeed, rose to a conception of the celestial and uni- 
versal atmosphere through the study of the terrestrial 
and local one. From the phenomena of sound, as dis- 
played in the air, they ascended to the phenomena of 
light, as displayed in the ether; which is the name given to 
the interstellar medium. 
The notion of this medium must not be considered as a 
* " Fortnightly Review," 1865, vol. iii. p. 129. 
