280 THE EVOLUTION OF SCIENTIFIC THEORIES 



original Copernican system to a strain ive recognize as utterly in- 

 tolerable. 



For a time Newtonian celestial dynamics proved superbly com- 

 petent to handle planetary observations of constantly improving ac- 

 curacy. Some minor aberrations presently observed in the motion of 

 the outermost planet were viewed with no great alarm for, as Dingle 

 emphasizes : 



Most scientific problems are relatively so superficial that anything so 

 drastic as a change in the basic terms of expression would be beyond 

 reason. When Uranus was found to move in a puzzling way, Adams 

 and Leverrier did not begin to reform the foundations of mechanics. 

 Rather than do that, they were prepared to call a new world into 

 existence [the subsequently discovered planet Neptune] to redress 

 the balance of the old, and they did so within the framework of cur- 

 rent mechanical theory. 



With still further accumulation of still more refined data, a much 

 smaller aberration in the motion of the innermost planet Mercury 

 became utterly inescapable. And, perfectly naturally, one then hy- 

 pothesized perturbations by an undiscovered inner planet, Vulcan— 

 a planet perhaps even unobservable because of its closeness to the 

 sun. Retrospectively we see that the behavior of Mercury strained 

 Newtonian dynamics, and signified its insufficiency. But contempo- 

 rary judgment showed, could have shown, no such awareness. For 

 how can one, at the time, distinguish between the ( sound ) Neptune 

 hypothesis and the (unsound) Vulcan hypothesis; between evidence 

 that further stretching of the theoretic pattern is needed and evi- 

 dence that it is already strained? Polanyi finds 



... no valid heuristic maxim in natural science which would recom- 

 mend either belief or doubt as a path to discovery. Some discoveries 

 are prompted by the conviction that something is fundamentally lack- 

 ing in the existing framework of science, others by the opposite feel- 

 ing that there is far more implied in it than has yet been realized. 



Manifestations of strain produced in other ways are, ordinarily, no 

 less equivocal. When Rumford demonstrated the continuous produc- 

 tion of heat in cannon-boring operations, we feel that the caloric 

 theory was not merely sti^ained but shattered. However, its adherents 

 merely introduced a plausible readjustment of their premises when 

 ive say they should have capitulated. In an exactly parallel circum- 



