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^t 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 wholly unconscious either, 

 for who does not know that a wdnd from the East or other 

 trivial circumstance will cause a surprising diff'erence 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 ; % 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 "Theorie des Ondes Lummeuses/' Saint Venant, Annales de 

 Chimie et de Physique, Mars, 1872, 



J In the A/tmalen of Poegendorf, abstracted in the Chemical Neus 

 of Sept. 13, 1872. 



