THE PHILOSOPHICAL BASIS 33 



at all events, prove a useful working hypothesis, 

 by the light of which research may be guided into 

 promising paths. As the range of observation 

 widens, and as the accuracy of the old observations 

 is increased, the fate of the new theory hangs in 

 the balance. The formula may, perhaps, still be 

 confirmed, it may require modification, or it may 

 have to be abandoned as a theory which has 

 played a useful and honourable part in its day, 

 but has become inadequate to express the develop- 

 ing knowledge of a later time. If so, it ceases to 

 be cited as an accepted theory. Not that Nature 

 has changed, but rather our attitude towards her, 

 and our conceptual model of her phenomena. 

 Thus new theories replace the old ones. 



Some years ago the constancy of the chemical 

 elements was, in the then state of knowledge, an 

 accepted theory. Latterly, the phenomena of 

 radio-activity have forced us to believe that 

 radium is passing continuously and spontaneously 

 into other elements — that true transmutations of 

 matter occur. The obvious transmutation of one 

 kind of matter leads to the possibility of the 

 gradual transmutation of all ; since as yet no 

 property of matter has been noted which is the 

 exclusive possession of one substance alone. New 

 phenomena, or rather phenomena for the first time 

 appreciated, are continually coming to light, and 

 evidence is accumulating from which the profit- 

 able construction of theories — for a time in abey- 

 ance — may again be pursued. Nothing must be 

 ruled out of court because contrary to received 

 views ; when a prima facie case has been made 

 out, everything must be examined by experiment, 

 induction, deduction, and again experiment. This 



D 



