508 The Velocity of Light. [.September, 
of matter to be audible must be of a certain size, which is 
diredtly obtained only by the mass motion of matter against 
coherent or contiguous matter. The vibrations of a tuning- 
fork within a vacuum are inaudible, yet they put the bell 
around in vibration, for they are seen. 
The denser a medium at equal elasticity, or the more 
elastic at equal density, the more rapidly it carries sound. 
But when sound is carried by light it travels still more 
rapidly, and yet it shall then be carried by a luminiferous 
ether infinitely less dense than our atmosphere. 
The emission, as well as the undulation, theory has occa- 
sionally predicted observations, for truth may be disguised 
in myths. The propagation of light does not require what 
we do not know, but atoms about which we know a little. 
Whereas Newton left it “ to the consideration of the reader 
if his agent,” leading matter according to the law of gravity, 
“ be material or immaterial”; the apostles of ether now 
call it matter. If it be matter in any state the propagation 
of light should, like that of sound, be connected with the g 
of the earth. Yet light is said to travel uniformly across 
the orbit of the earth from the moons of Jupiter and the 
most distant stars, and from any generator to any receiver 
whatsoever, unless within our atmosphere. Yet attraction 
vastly decreases through these spaces, and depends on mass. 
The velocity of light should also be influenced by the g of 
the mass from which it starts. The density of ether — in- 
different if it be gaseous, liquid, or solid — could not be 
uniform between the generator and receiver of light. 
According to some the ether is an undivided rigid solid. 
How could it undulate, having no internal elasticity, no 
space for motion ? how could it be pierced regardless of the 
propelling and resisting force, according to the theory of 
emission ? 
The velocity of sound is measured by elasticity of tan- 
gible matter ; but who shall measure the elasticity of what 
nobody ever felt, saw, and caught, or intelligibly described ? 
According to others ether is a contiguous liquid, moving 
with “ infinite ” rapidity in vortices within bounded spaces, 
now carrying all sorts of matter along, now passing through 
it, now surrounding it through vastest spaces with undensest 
density, now jammed and compressed between its mole- 
cules. 
The liquid shall, revolving in closed spaces or in a finite 
universe, become an absolutely rigid liquid. A number of 
entertaining experiments shall even prove this stupendous 
theoryr A bounded universe within infinity is an absurdity ; 
