ROYAL IRISH ACADEMY. 
213 
back nor penetrate. That this may he so, the outward motion of the 
superficial layer of molecules of the medium must meet with an absolute 
obstruction from the repulsion of the inner layer of molecules of the con¬ 
taining vessel. The forces thus coming into play would be at variance 
with hypothesis (4); on which account it is needless here to trace further 
the consequences of their action, several of which are, besides, sufficiently 
obvious. 
This kind of examination might, indeed, be continued almost inde¬ 
finitely, and extended to the crystalline texture of the medium and other 
branches of the subject; but enough has been done for my present 
end, which is to draw attention to the fact, that no known ponderable 
material possesses a constitution of the kind which has been supposed, 
and, consequently, that we are forced to admit, as demonstrated, the 
following points with reference to this obscure branch of Physics :— 
1°. That no known ponderable matter consists of a continuous sub¬ 
stance similar in all its parts. 
2°. That by continuing the subdivision of solids, as far as is consistent 
with the parts being similar, similarly placed, and acting alike, either 
the whole, or at least a controlling part, of the action on each such mole¬ 
cule must be contributed by a finite number of those in its vicinity. 
The validity of this conclusion is not disturbed by attributing to the 
elementary molecules such motions as may constitute sound, heat, light, 
and electricity, and the statement is evidently d fortiori true of the parts 
of the elementary molecules. 
3°. If liquids are separable into elementary molecules of the kind 
described in the last paragraph, similar to one another, similarly placed 
and acting alike, then the statement of that paragraph may be repeated, 
word for word, with reference to them; but if, as seems perhaps more 
likely, there is going on between the elementary molecules of liquids a 
constant interchange of their parts, then the language must be somewhat 
modified, although the conclusion remains substantially the same. 
The case of gases is somewhat different. The examination which 
has been made above shows, no doubt, in the case of gases, as it does for 
either solids or liquids, that their constitution cannot be that of a sta¬ 
tionary system, each molecule of which acts, but to a trifling extent, on 
each of those around it. But it does not show that it may not be such 
a system in a state of vivid molecular motion. The closer investigation 
of this hypothesis opens a new branch of the subject. Already, how¬ 
ever, a positive step appears to have been made by demonstrating that 
in solids and liquids each molecule is acted on to a finite extent by those 
in its immediate neighbourhood. 
Sir William R. Hamilton read a paper, “ On some Transformations 
of Diverging Lines.” 
A collection of twenty-five ancient articles, consisting of bronze pins . 
of several forms, the axis of a spinning bobbin, and two needles, all found 
near Gweedore, county of Donegal, were presented. 
vol. v. — proc. soc. 2 p 
