The Domain of Physical Science 199 



and the answer 1 6*5 seconds — that is to say, the difference of two 

 pointer-readings on the seconds'-dial of our watch. 



Leaving out all aesthetic, ethical, or spiritual aspects of our 

 environment, we are faced with qualities such as massiveness, sub- 

 stantiality, extension, duration, which are supposed to belong to 

 the domain of physics. In a sense they do belong ; but physics is 

 not in a position to handle them directly. The essence of their 

 nature is inscrutable ; we may use mental pictures to aid calcula- 

 tions, but no image in the mind can be a replica of that which is 

 not in the mind. And so in its actual procedure physics studies 

 not these inscrutable qualities, but pointer-readings which we can 

 observe. The readings, it is true, reflect the fluctuations of the 

 world-qualities ; but our exact knowledge is of the readings, not of 

 the qualities. The former have as much resemblance to the latter 

 as a telephone-number has to a subscriber. The triumph of 

 exact science in the problem just quoted consisted in establishing 

 a numerical connection between the pointer-reading of the weigh- 

 ing machine in one experiment on the elephant and the pointer- 

 reading of the watch in another experiment. The elephant itself 

 as an object in the external world was only an intermediary, and 

 no knowledge of the kind called exact could be asserted about it. 



Perhaps it will seem that a great deal of knowledge about the 

 elephant itself is implicitly contained in a knowledge of these 

 readings occurring in the various kinds of experiments that can be 

 made on it ; that indeed a knowledge of the response of the various 

 objects of the world — weighing-machines and other indicators — 

 to the presence of the elephant is the most complete knowledge of 

 the elephant we could desire. As a relativist I accept this theory of 

 knowledge ; but it should be realised that it transforms our view of 

 the nature and status of physical knowledge in a fundamental way. 

 Until recently physicists took it for granted that they had knowledge 

 of the entities dealt with, which was of a more intimate character ; 

 and the difficulty which many find even now in accepting the theory 

 of relativity arises from an unwillingness to give up these intuitions 

 or traditions as to the intrinsic nature of space, time, matter, and 

 force, and substitute for them a knowledge expressible in terms of 

 the readings of measuring instruments. In considering the rela- 

 tions of science and religion it is a very relevant fact that physics 

 is now in course of abandonmg all claim to a type of knowledge 

 which it formerly asserted without hesitation. Moreover, these 



