ELISHA MITCHELL SCIENTIFIC SOCIETY 13 
any law underlying the gradation in the properties of the 
elements with the increase of atomic weights, are some of the 
difficulties. In comparing these two hypotheses that of 
Graham seems to me very improbable. I have thought of 
valence as dependent upon the character of the motion of the 
atom, but cannot well conceive of a similar dependence of 
atomic weight and all the other properties. ‘There remains, 
then, the hypotheses of primal elements by the combination 
of which our elements have been formed. ‘These molecules 
are probably distinguished from the ordinary molecules by 
the actual contact and absolute union of the ia ica atoms 
without the intervention of ether. 
Since these elemental molecules cannot as yet be divided, 
we may retain the name atom for them, but the idea of sim- 
plicity and homogeneity no longer belongs to them. The 
definition of an element as a body made up of similar atoms 
is equally lacking in fidelity to latest thought and belief, but 
chemists would scarcely consent to change it, and, indeed, it 
may well be retained provided the modified meaning is given 
to the word atom. But, after all, an element is best defined 
by means of its properties, It is by close study of these that 
we decide upon its elemental nature, and through them it is 
tested. Complete reliance can no longer be placed upon the 
balance and the supposed atomic weight. 
All elements are acted upon by gravity and chemical force 
and other physical forces, but within the last few years cer- 
tain gaseous elements have been discovered which are not in- 
fluenced by chemical force or affinity, According to some 
(Piccini, Zezts. An. Chem. X1X, 295) this necessitates a divis- 
ion of the elements into two classes. Manifestly, since it is 
chiefly by the action of chemical force that we study the ele- 
ments, the absence of such action cuts us off from our chief 
means of finding out anything about them, and it is equally 
clear that bodies so diverse cannot well be classified together. 
If all attempts at bringing about the chemical union of these 
gaseous elements with other bodies fail, I believe that we 
should insist upon the existence of two classes of elements 
and keep them distinct in all comparisons. 
