124 REPORTS ON THE STATE OF SCIENCE. 



the Archives of Paris or the double royal cubit of the Temple of Karnac. 

 No theory of evolution can be formed to account for the similarity of 

 atoms, for evolution necessarily implies continuous change, and the atom 

 is incapable of growth or decay, of generation or destruction. 



' On the other hand, the exact equality of each atom gives to it, as 

 Sir John Herschel has well said, the essential character of a manu- 

 factured article, and precludes the idea of its being eternal and self- 

 existent.' 



In this quotation we have the best generalised expression of the 

 philosophy of a generation ago. To-day we could deduce even more 

 striking examples of the exact similarity of atoms than were then known, 

 and yet we believe in evolution as an experimentally demonstrated fact. 



A little later the swing of the pendulum was again towards some 

 system of evolution. The discovery of the periodic law, and the natural 

 order into which the elements fell when classed according to their atomic 

 weight, the recurrence periodically of elements resembling each other in 

 properties, these resemblances extending even to similarity of spectrum, 

 together with the growing knowledge of all that the spectrum of an 

 element implied, led to the view that similar elements must possess similar 

 structures, in which the constituent stuff out of which they are built 

 is the same but the quantity and arrangement different in the formation 

 of each atom. The idea was expressed, by the lemniscate curve of Sir 

 William Crookes, that the elements were successively formed out of the 

 same protyle, while in their formation a periodic change of the conditions 

 conditioned the periodic recurrence of properties. A little later Sir 

 Norman Lockyer propounded a theory of inorganic evolution accompany- 

 ing cosmical evolution, in which in the hottest stars it was concluded the 

 conditions are such that only the lighter elements can exist, and then, as 

 the star cools, the heavier elements successively make their appearance, by 

 the condensation of the lighter. 



Finally we have the brilliant series of researches emanating from the 

 Cavendish Laboratory, under J. J. Thomson, in which he succeeded in 

 the isolation and measurement of the constants of the corpuscle or 

 negative electron, and the recognition that this must possess the 

 fundamental attribute of matter, inertia or mass. From this point came 

 the step to the conclusion that negative electricity might be the protyle, 

 out of which all atoms are in some way constructed, by varying numbers 

 being combined together in stable systems in regular motion. But in the 

 more purely speculative part of this theory it is not necessary for me to 

 venture. 



I pass to the discovery of the radioactivity of matter by Becquerel 

 and its essential characteristic, which at once arrested attention. Here 

 we had a case of certain of the heaviest elements being proved continually 

 to liberate energy of a very novel and striking character without at first 

 sight any perceptible change in the matter or any exhaustion of the 

 supply. As is well known, this energy is manifested in the emission 

 of new sorts of radiation, and it has been proved that these radiations are 

 in nature much what Newton supposed light to be, consisting of streams 

 of material particles ejected from the matter with hitherto unknown 

 velocities. In general two kinds of radiant particles have been recognised, 

 the n particle, having a mass slightly greater than the hydrogen atom, and 

 the f) particle, which is an electron or corpuscle many thousand times 

 smaller. 



