254 THE HISTORY OF SCIENCE 



gested this assumption of a primitive matter, protyl, 

 from which all other substances were derived. In the 

 light of the corpuscular theory as well as of the trans- 

 formation theory it seems possible that the helium 

 atom and the negative corpuscle will offer a clue to 

 the genesis of the elements. 



What is to be learned from this rapid sketch, of 

 the discovery of the radioactive substances, concern- 

 ing the nature and value of scientific hypothesis? 

 For one thing, the scientific hypothesis is necessary 

 to the experimenter. The mind runs ahead of and 

 guides the experiment. Again, the hypothesis sug- 

 gests new lines of research, enables one in some cases 

 to anticipate the outcome of experiment, and may be 

 abundantly justified by results. " It is safe to say," 

 writes Rutherford, " that the rapidity of growth of 

 accurate knowledge of radioactive phenomena has 

 been largely due to the influence of the disintegration 

 theory." The valid hypothesis serves to explain facts, 

 leads to discovery, and does not conflict with known 

 facts or with verified generalizations, though, as we 

 have seen, it may modify other hypotheses. Those 

 who support a hypothesis should bring it to the test 

 of rigid verification, avoiding skepticism, shunning 

 credulity. Even a false assumption, as we have seen, 

 may prove valuable when carefully put to the proof. 



The layman's distrust of the unverified hypothesis 

 is in the main wholesome. It is a duty not to believe 

 it, not to disbelieve it, but to weigh judicially the evi- 

 dence for and against. The fact that assumption plays 

 a large part in our mental attitude toward practical 

 affairs should make us wary of contesting the legiti- 

 macy of scientific hypotheses. 



