THE NATURE OF REALITY 443 



a swarm of gnats than a substantial object. 1 The specula- 

 tive problem begins, therefore, not with the fact of objects 

 but with the fact of duplicate objects. There is not only 

 heat but molecules, not only substantiality but disembodied 

 electric charges, not only colors but electro-magnetic waves. 

 What prove to be the real data upon which the speculative 

 problem builds, however, are certain facts pertaining to the 

 relation between these realms. The task of science is that of 

 constructing a world which is to be symbolic of the world of 

 commonplace experience. 2 This must be a "world which 

 will imitate the actual behavior of the world of familiar 

 experience." 3 Using the word "infer" in a somewhat broad 

 sense science may be said to infer its description of the 

 external world from the facts of sense experience. 4 This 

 determines an important relation between the realms. In 

 the vocabulary of the physicist one finds such words as 

 "length," "angle," "velocity," "force," "potential," "cur- 

 rent," etc., which are called "physical quantities." It is now 

 being asserted that these should be defined no longer in terms 

 of any metaphysical significance which may have been 

 attached to them but according to the way in which they 

 are actually identified when we are confronted with them. 5 

 But how do we recognize them? By reading scales, dials, 

 clocks, and other measuring devices. In other words the en- 

 tities of science prove to be nothing but pointer readings 

 on recording instruments. Eddington's famous illustration 

 of the method of science in the problem concerning the ele- 

 phant sliding down the grassy hillside has already been 

 quoted. 6 All of exact science consists of similar pointer 

 readings and other indications on instruments. The concep- 

 tions of objects which function in our common view of the 

 world do not enter into exact science. Science must replace 

 such conceptions by quantities representing the results of 

 physical measurement. 7 



1 New Pathways in Science, p. 1. B Nature of the Physical World, p. 254. 



2 Nature of the Physical World, p. xiii. 6 Pp. 15-16. 



3 Ibid., p. 249. 7 Ibid., p. 253. 



4 New Pathways in Science, p. 9. 



