determinations, the more probable it seemed that in reality cobalt, and not nickel, as demanded by theory, has the greater weight. The whole subject has been very carefully investigated in the last few years by Prof. Theodore W. Richards at Harvard University, and there seems now to be no doubt but that Nature has unexpectedly and inexplicably reversed the position of these elements.
Another instance that seems to be of the same nature is that as far as the most accurate determinations go, tellurium has an atomic weight greater than that of iodin, instead of less. At present it is impossible to explain these abnormalities, but they assure us of the possibility that argon may have a higher atomic weight than potassium, and yet belong to the eighth group.
What now is the present position of the philosophy of matter from the light thrown upon it by the Periodic Law? In the first place, drawing our deduction from the marvelously accurate determinations of. the relative weights of the atoms of the different elements, to which chemists have been incited by the Periodic Law, it may be considered as absolutely settled that the elements are not groups of hydrogen atoms, nor are they composed of half or quarter hydrogen atoms. As enunciated by Prout, the hypothesis which goes by his name may be considered as finally proved untenable; the atomic weights are not multiples of the weight of the hydrogen atom, nor any simple fraction thereof. But while this is the case, it is perfectly clear from the Periodic Law that the properties of an atom are a periodic function of its atomic weight. It would seem that this can be true only if the material of which all atoms are made is the same. This does not necessarily mean that there is but one kind of matter, and that all atoms are merely different quantities of this 'urstoff.' There may be several kinds of matter, and different kinds of atoms may represent varying proportions of a few constituents.
There have been many attempts to reduce the Periodic Law to mathematics, in order to find a numerical value for the function which expresses the relation between atomic weight and an element's place in the series. Such efforts have been thus far wholly unsuccessful. It is by no means impossible that such relations will be found in the future, but at present the atomic weights of comparatively few elements have been determined with great accuracy. When this work has been extended to a greater number of elements, and when the position of the rare elements and of the inert atmospheric gases has been definitely settled, we may hope for more light upon the principles underlying the Periodic Law.
At present this law occupies much the same position as two other great generalizations of natural science. The fact of gravitation was long ago discovered. The laws by which it acts are well known, and
