336 
36. The luminiferous ether must then exceed in bulk that of 
material substance as much as the interstellar spaces exceed the 
bulk of the stars Themselves. All this must be filled by self- 
repulsive and (thence) elastic atoms of ether whose distance one 
from the other must be almost inconceivably small. The thick- 
ness of a soap-bubble before it bursts has been proved to be 
only four ten-millionths of an inch, but the inference deduced 
from the waves of light is that the mean distance of the atoms 
of ether must be less than one ten-millionth of an inch.* If 
these figures present difficulty we are only at the commence- 
ment of our troubles, for another difficulty must be overcome 
in the conception of this great scientific fact, since profound 
investigators such as Fresnel and Cauchy are, led to suppose 
from the character of its vibrations that the notion under 
which we must conceive of it is an immense imponderable solid 
of the same elastic contexture in all directions, as well in the 
interior of crystals as in the air, glass, f &c. So that the Latin 
word firmamentum, — English, firmament, — comes to be, after 
all, though quite accidentally, the best description of the vault' 
of heaven above us. 
37. Within us also must this subtle substance penetrate, having 
most intimate relations with us, though we are all unconscious 
of its presence ; and yet perhaps not w'holly unconscious either, 
for who does not know that a wind from the East or other 
trivial circumstance will cause a surprising difference in our 
sensations- — in no way to be accounted for but by some varia- 
tion in the agent which we call electricity. 
38. It is impossible to overrate the importance of the know- 
ledge of light and its undulations to the chemist. By means of 
these he is enabled to discern, with more or less certainty, the 
composition of the sun and of other heavenly bodies, and to 
derive information, not otherwise to be obtained, concerning 
substances of earthly mould. I will only mention one kind of 
research which illustrates the connection of Part III. of my 
argument with Part II., or the relation of ethereal vibrations to 
the vibrations of ponderable matter. 
39. I refer to a recently published paper by Professor Lom- 
mel, on the relation of chlorophyll to light ; J apologizing for 
the abstract character of the chemical statements. It seems 
requisite to my argument to show by one instance out of many, 
* Birks on Matter and Ether , p. 18. 
t Vide “Th4orie des Ondes Lumineuses/’ Saint Venant, Annales de 
Chimie et de Physique, Mars, 1872. 
1 In the Annalen of Poggendorf, abstracted in the Chemical News 
of Sept. 13, 1872. 
