1874.] Atomic Matter and Luminiferous Ether. 189 
circumstances with other vibratory motions, as light and 
radiant heat. Hence, two gases diffused through each other 
possess a quality which is not the average of the same gases 
alternated in small bulks, but which appears to be of a 
distinct kind. No evident solution of this problem occurs 
on the atomic theory. If ether permeate all bodies, and be 
the medium of transmission, it is both a conductor and non- 
conductor of electricity, both opaque and transparent to 
light, both diathermous, anda heat-absorbent; but as this 
is an evident absurdity, the utmost transparency of solids 
and fluids to light, radiant heat, electricity, sound, &c., is 
due to unbroken atomic continuity in at least one dire¢tion. 
But the metal potassium before alluded to is a conductor of 
electricity, and, therefore, its substance is continuous. 
‘Faraday, however, showed that 680 parts of it together 
with 2744 units of other substances could be compressed 
into less space than was originally filled with 430 parts of 
potassium itself; and it is difficult to avoid the conclusion 
that potassium is elastic; and, if potassium, then all other 
bodies—solid, fluid, and gaseous. 
It is difficult to trace mentally the act of elastic disturb- 
ance within the substance of a body, but this difficulty is 
equally great with ether, and not more difficult with tangible 
than with intangible matter, and it is more in accordance 
with scientific method to connect a known or evident 
property with a known substance which exhibits similar 
qualities, than with an unknown substance whose mere 
existence is hypothetical. 
Attraction of cohesion, one of the most evident properties 
of atomic matter, is intimately related to elasticity ; but the 
atomic theory does not explain how. As the present object 
is rather to criticise an existing theory than to construct a 
new one, it is unnecessary to account for what the atomic 
theory leaves obscure ; but it is somewhat probable that the 
true explanation lies in a direction we proceed very incom- 
pletely to indicate: mechanically, motions that coincide 
coalesce without jarring or ‘‘interference;’? motions that 
do not coincide jar and tend to separate. 
Another experiment of Tyndall’s exemplifies these remarks. 
Holding a glass tube of about six feet long, and two inches 
diameter by its middle, he rubbed one end of it with a wet 
cloth and caused it to emit the sound of a musical note from 
the longitudinal vibrations thus excited. The free end of 
the tube was shaken into pieces; each piece a ring, and 
many of. them with cracks quite round the tube, but not 
completely through its substance. It would require a 
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