THEORIES AND MODELS 251 



The model ... is not the same as the thing or process it models; 

 it is analogous to the metaphor. The interpretation by model is 

 partial. But this lack is compensated by the requirement that the 

 model, in fact, must not be a complete interpretation since we want to 

 introduce, with its help, new concepts and construct a higher theory. 

 Mechanical models cannot, and must not, completely interpret, 

 e.g., electromagnetism, since we need room for new concepts, like 

 charge. 



We must not then take a theoretic model too literally; indeed, loe 

 may err by taking the model too literally. But, as we would realize 

 the full heuristic power inherent in it, we must take the model very 

 seriously. Pascal's idea of a distinct upper surface to the atmosphere 

 is a misconception born of taking Torricelli's model too literally, but 

 the Puy de Dome experiment is conceived only as that model is taken 

 in dead earnest. 



Our models may lead us far astray: we cannot always distinguish 

 "amply seriously" from "too literally." Observing, with Duhem, that 

 these explanatory "superfluities ' are often the least enduring features 

 of our theories, we may be led to adopt the positivists' cynical ap- 

 praisal of physical models and analogies. That attitude denies us the 

 full usefulness of these heuristic devices. If our models are to lead us 

 to ask, and seek answers for, new questions about the world, we must 

 regard them as something more than "logical superfluities," "illicit 

 attempts at explanation," "convenient fictions," or the like. The lesson 

 of scientific history is unmistakable. To the hypothetical entities 

 sketched by our theories we must venture at least provisional grants 

 of ontologic status. Major discoveries are made when invisible atoms, 

 electrons, nuclei, viruses, vitamins, hormones, genes are regarded as 

 existing. De Santillana comments that: 



When Leverrier found Neptune "at the tip of his pen," as panegyrics 

 said, he was not simply looking for an economic regularizing entity- 

 he was thinking of a new planet. 



Polanyi strongly underlines the point with a citation of a more recent 

 example: 



One of the greatest and most surprising discoveries of our own age, 

 that of the diffraction of X-rays by crystals (in 1912) was made by a 

 mathematician, Max von Laue, by the sheer power of believing more 

 concretely than anyone else in the accepted theory of crystals and 

 X-rays. 



