94 WHAT IS SCIENCE? 



is a greater achievement than the formulation of a new 

 law, I cannot admit that the two processes are essentially 

 different. As Galileo was the founder of experimental 

 physics, so Newton was the founder of theoretical physics ; 

 as Galileo first introduced the type of law which has 

 become most characteristic of the science, so Newton 

 introduced first the characteristic type of theory. And 

 of the two Newton is rightly judged by popular opinion 

 to have been the greater man. But it is not rightly 

 recognized how great was the acnievement of Galileo ; 

 indeed his fame is usually associated with things the 

 observation of the isochronism of the pendulum, or his 

 fight with clericalism over the Copernican theory 

 other than with his greatest service to science. It is 

 his establishment of the first experimental numerical 

 law that constitutes his highest claim to greatness, and 

 that law was as much an expression of his personality 

 as the theory of Newton. 



THE ANALOGIES OF THEORIES 



Mention has just been made of " types " of theories. 

 There are such types, just as there are types of laws, 

 and they play the same role in permitting lesser men to 

 complete and extend the work of the greater. Once a 

 theory of a new type has been invented and has been 

 shown to be true in the explanation of laws, it is naturally 

 suggested that similar theories may prove equally 

 successful in the explanation of other laws. And on the 

 whole the suggestion has proved true. In each branch 

 of science there are certain very broad and general 

 theories which have been invented by the founders of that 

 branch ; subsequent development of that branch usually 

 consists largely in the ampliation and slight modifica- 

 tion of such fundamental theories by investigators, 

 many of whom could never have themselves laid the 



