10 REPORT—1905. 
Even when the working model has been successfully imagined, this latter 
task may often overtax the powers of the mathematician. Finally it 
remains for him to apply his results to actual matter, and to form a 
judgment of the extent to which it is justifiable to interpret Nature by 
means of his results. 
The remainder of my address will be occupied by an account of 
various investigations which will illustrate the principles and methods 
which I have now explained in general terms. 
The fascinating idea that matter of all kinds has a common sub- 
stratum is of remote antiquity. In the Middle Ages the alchemists, 
inspired by this idea, conceived the possibility of transforming the baser 
metals into gold. The sole difficulty seemed to them the discovery of an 
appropriate series of chemical operations. We now know that they 
were always indefinitely far from the goal of their search, yet we must 
accord to them the honour of having been the pioneers of modern 
chemistry. 
The object of alchemy, as stated in modern language, was to break 
up or dissociate the atoms of one chemical element into its component 
parts, and afterwards to reunite them into atoms of gold. Although even 
the dissociative stage of the alchemistic problem still lies far beyond the 
power of the chemist, yet modern researches seem to furnish a suffi- 
ciently clear idea of the structure of atoms to enable us to see what 
would have to be done to effect a transformation of elements. Indeed, in 
the complex changes which are found to occur spontaneously in uranium, 
radium, and the allied metals we are probably watching a spontaneous 
dissociation and transmutation of elements. 
Natural Selection may seem, at first sight, as remote as the poles 
asunder from the ideas of the alchemist, yet dissociation and transmuta- 
tion depend on the instability and regained stability of the atom, and 
the survival of the stable atom depends on the principle of Natural 
Selection. 
Until some ten years ago the essential diversity of the chemical 
elements was accepted by the chemist as an ultimate fact, and indeed the 
very vame of atom, or that which cannot be cut, was given to what 
was supposed to be the final indivisible portion of matter. The chemist 
thus proceeded in much the same way as the biologist who, in discussing 
evolution, accepts the species as his working unit. Accordingly, until 
recently the chemist discussed working models of matter of atomic 
structure, and the vast edifice of modern chemistry has been built with 
atomic bricks. 
But within the last few years the electrical researches of Lenard, 
Roéntgen, Becquerel, the Curies, of my colleagues Larmor and Thomson, 
and of a host of others, bave-shown that the atom is not indivisible, and 
a flood of light has been thrown thereby on the ultimate constitution of 
