between the Atomic Weights. 403 
likewise, though the noblest of metals, yet in some of its chemi- 
eal relations resembles much more closely the members of the 
Nine than of the Four Series, and here again its accommodating 
atomic weight seems to account for its double-sided character. 
Several other examples of similar affiliations are given in the 
table, but do not need explanation. 
In the description just concluded of the classification of the 
chemical elements, which is offered in this memoir, I have not 
eltered into details, for to have done so would have been to write 
a treatise on chemistry. I have confined myself almost exclu- 
sively to general points, and referred only to those particulars 
which I thonght might present doubts. I hope that I have been 
able to show, first, that the chemical elements may be classified 
in a few series similar to the series of homologues of organic 
chemistry ; second, that in those series the properties of the ele- 
ments follow a law of progression; and finally, that the atomic 
Weights vary according to a similar law, which may be expressed 
bya simple algebraic formula. As already intimated, I have en- 
deavored to prove the correctness of the classification on general 
grounds, in order that it might appear that the simple numerical 
relation which has been discovered between the atomic weights 
is not a matter of chance, but is connected with the most funda- 
Mental properties of the elements.- I might leave the subject at 
this point, but the existence of the law which I wish to establish 
will be proved more conclusively if it can be shown, not simply 
that the general properties of the members of each series vary in 
a reguiar manner, but also if in one or more cases the exact law 
of the variation can be pointed out. 
There are but few properties of the elements which are sub- 
jects of measurement, aud which therefore can be compared nu- 
Merically. Such are the specific gravity in which the three states 
of aggregation, the boiling and melting points, the capacity of 
heat, and a few others. It is easy to see tnat there are but few 
of these properties the law of whose variation in the series we 
could reasonably expect to discover in the present state of science. 
ost of them evidently depend upon molecular forces with which 
We are entirely unacquainted. Such in solids is undoubtedly the 
case with so simple and fundamental a property as specific gravity, 
and most, if not all, of the other properties of solids belong to 
the same category. It cannot therefore be expected that we 
should point out the laws by which these properties vary, altthongh 
the remarkable investigations of Kopp, Dana, Filhol, Schréder, 
and others, on the relations between the density of substances 
and their atomic weights, and those of Kengott on the relation 
rdness to atomic volume, give grounds for expecting that 
€ven they will before long be discovered. In liquids and gases, 
however, most of these molecular forces which produce the ap- 
