56 THE PATH OF SCIENCE 



the relativity theory of Einstein appeared completely absurd 

 when introduced. Ralph Fowler wrote in Nature in 1934, 

 "Nothing could have exceeded the apparently wild extrava- 

 gance of de Broglie's first work on electron waves which led 

 directly to quantum mechanics." This does not mean that 

 the formulator of a scientific theory would try to make his 

 theory appear absurd or contrary to common sense. It means 

 only that common sense has nothing whatever to do ^vith 

 scientific theorizing or with the practice of scientific research. 

 Common sense is a judgment depending on common beliefs 

 rather than logic. As Enriques says, "It is a prudent safe- 

 guard for whoever w^ants to spare himself the critical study 

 of scientific expressions." * 



In an analysis of the part played by theory in the develop- 

 ment of science, Margenau f divides the world of the scien- 

 tist into two parts: sense data and constructs. The sense 

 data we have discussed as facts or coincidence data; the con- 

 structs are concepts invented by certain rules and bearing 

 certain relations to sense data. We look at a line in the 

 spectrum and say that it is blue. We associate this blueness 

 with the existence of light and of light of a certain wave 

 length. These ideas are constructs. Other constructs are, in 

 mathematics, number^ integral, space; in chemistry, element j 

 atom, compound, valence bond; in physics, electron, electric 

 field, mass. The ideas that form the body of scientific knowl- 

 edge deal primarily wdth these constructs, which represent 

 sense data symbolically and have properties that permit their 

 discussion logically and wdth the aid of mathematics. These 

 are a scientist's operations: 



The scientist assembles his facts, he translates his data into 

 constructs that he invents for the purpose according to cer- 

 tain rules that experience has shown to be useful. He then 

 assembles these constructs, frequently using the language and 



* Enriques, Problems of Science, English translation, p, 329, London, 

 1924. (Quoted by George, op. cit., p. 247.) 



f H, Margenau, "Theory and Scientific Development," Scientific 

 Monthly, LVII, 63 (1943). 



