38 THE REALITIES OF MODERN SCIENCE 



the steps traced above. It sometimes happens that a 

 theory is apparently completely verified and for genera- 

 tions commonly accepted by the scientifically trained. 

 Later some experimental evidence may come to notice 

 which explodes the existing theory. The new theory 

 which arises to take into account the exceptions to the 

 previously accepted theory must, however, fight its 

 way against a natural conservatism and even against the 

 opinions of scientists whose other achievements have 

 entitled them to great influence. 1 



In the case of the Greek scientists or rather philoso- 

 phers, the tendency was to advance broad general 

 theories, like that of Thales, without applying to them 

 the check of experiment. Of course, if by experiment 

 we can learn how some natural phenomenon occurs, 

 we no longer need a " theory" to account for it, nor 

 need we build our explanation upon a " hypo thesis." 

 On the other hand, checking a theory by experiment 

 does not indicate the correctness of all the assumptions 

 but merely that they will account for all the observed 

 facts of the experiment. 



Forming theories is then one of our methods -of 

 learning the explanation of the phenomena which 

 attract our attention. Without curiosity as to the 

 "why" of the various aspects of the world about us 

 we make but slight progress. The Greeks had an 

 unflinching curiosity. Although most of their physical 

 theories have since proved wrong, the curiosity which 



1 In the struggle between the wave theory of light and the pre- 

 ceding corpuscular theory the opinion of Newton greatly retarded 

 the common acceptance of the former. The classical example is, 

 of course, the astronomical theory of Ptolemy. 



