Correspoudence. 401 
miscibility with our atmosphere, like oil with water—a 
quality not entirely adverse to experience nor repugnant 
to reason. The question, then, naturally arises, what be- 
comes of the waves of heat and light when they reach our 
atmosphere ?—and is ordinary matter sufficient and effectual 
for this transmission? ‘This question can be answered only 
by analogy, which appears to infer an affirmative. 
That sound waves are transmitted by air, and not by 
interstitial ather, is unquestionable; and if air be capable 
of transmitting 25,000 vibrations in one second, it would 
probably be difficult to assign any valid reason why the 
same medium is incapable of transmitting the far more 
rapid waves of heat and light; and if incapable, then 
where lies the necessity for assuming the presence of 
another medium : ? 
Again, the refraction of sound, as demonstrated by fie 
experiments ef), Hajech and Sondhans (565, 564), is in 
exact accordance with the laws hitherto assigned to the 
refraction of light and heat. But the phenomena of the 
refraction of light require a very forced addendum to the 
interstitial-zether-hypothesis—namely, that the elasticity of 
the zther zs dependent upon that of the medium which tt 
pervades—an unprecedented influence of one kind of matter 
on other merely contiguous matter. And it appears that 
the velocity of sound in solid and liquid is much greater 
than in air (545); in water it is nearly 5,000 feet, and in 
iron nearly 17,000 feet in one second: is there, then, any 
known fact whatever that tends to assign a limit to the 
possible velocity of transmission of wave-motion through 
those and other material media? If not, then the presence 
of ether, as generally assumed, cannot be deemed 
essential to the transmission of light; and if not essential, 
why should the old hypothesis be entertained ? 
“Nec Deris intersit nisi digures vindrie nodus 
Inciderit.” 
Moreover, Professor Tyndall, to whom the progress of 
dynamical physics is indebted for many laborious and im- 
portant researches, has observed that in various kinds of 
wood there is a remarkable harmony between their re- 
spective conductivities for sound and heat in three mutually 
perpendicular directions—namely, longitudinal, transverse- 
radial, and transverse-tangential (546).. Now, although 
there is certainly no direct analogy between the conduction 
of heat and the radiation of light, beyond that of their 
