ON THE EVOLUTION OF THE ELEMENTS. 123 



trend of philosophic thought. We are now, however, more nearly con- 

 cerned with the lines of attack at our disposal for dealing with the new 

 situation which has presented itself, and in which, it must be confessed, 

 we feel unusually ill-equipped. The weapons available are rather limited 

 in their range, and there is the possibility that the radio- elements may 

 remain for long the only example of a process of evolution which we 

 cannot but believe will ultimately embrace all the elements within its 

 scope, and lead to a consistent theory of the whole material universe. 



More than fifteen hundred years ago, as M. Berthelot has pointed out, 

 the symbol by which matter was every vvhere expressed was a serpent, 

 the body coiled into a circle and the head devouring the tail, bearing the 

 central motto ' ev to Trav.' This was derived from the Greeks, who, in 

 imagination, untrammelled by knowledge, far surpassed even the most 

 advanced theory of to-day, supposing that material evolution proceeded 

 in a cycle, and thus were able to arrive intuitively at a system at once 

 continuous, consistent, and eternal, avoiding the inherent difficulties con- 

 nected with the beginning and end of the process which trouble us to-day. 

 From that time till quite recently, although the idea of continuous 

 evolution of matter was never absent, experimental knowledge advanced 

 steadily along lines which seemed almost to disprove the possibility of 

 any such process. We had Boyle's recognition of an element as a sub- 

 stance which could not be fundamentally changed or made to yield 

 anything more simple, and the continued existence of a relatively few 

 constituent elements throughout all chemical changes. The law of 

 multiple proportions and Dalton's atomic theory led to the idea of atoms, 

 in their modern experimental sense, as the units of all chemical changes — 

 the bricks, so to speak, out of which all molecules are built and into 

 which they can be resolved. The advent of the spectroscope and the 

 evidence afforded by such meteorites as make their way to us from dis- 

 tant regions proved the essentially uniform composition of the material 

 universe. 



Intimately connected with these researches another idea took shape 

 as chemistry advanced. Not the slightest variation in the properties of 

 elements could be detected, and hence each atom must be exactly like 

 every other of any one element. It had constants, such as the atomic 

 mass, which is in itself a theoretical abstraction from the experimental 

 combining or equivalent weight, and periods, represented by the character- 

 istic lines in its spectrum, capable of being measured with extreme 

 accuracy, and in which the slightest variation in value had never been 

 detected. An atom of hydrogen executes its vibrations, by which we 

 know it, at precisely the same rate in the most distant star as in the 

 laboratory. This seemed to exclude the possibility of a gradual change 

 or evolution of one element into another. The position cannot be more 

 forcibly expressed than in the familiar words of Clerk Maxwell to this 

 Association at the Bradford Meeting in 1873. 



' In the heavens we discover by their light, and by their light alone, stars 

 so distant from each other that no material thing can ever have passed 

 between them, and yet this light tells us also that each of them is built 

 up of atoms ' of the same kind as those we find on earth. 



' . . . Each atom, therefore, throughout the universe bears impressed 

 upon it the stamp of a metric system as distinctly as does the metre of 



' I have replaced the word molecule throughout by atom, so as to retain the same 

 meaning for the word atom as it bears throughout the paper. 



