i 4 DOWNFALL OF CLASSICAL PHYSICS 



has them, alas ! but he cannot make real use of them. 

 So when he speaks of space it is always the inches or 

 pints that he should have in mind. It is from this point 

 of view that our space and the space of the nebular 

 physicists are different spaces; the reckoning of inches 

 and pints is different. To avoid possible misunder- 

 standing it is perhaps better to say that we have different 

 frames of space — different frames to which we refer the 

 location of objects. Do not, however, think of a frame 

 of space as something consciously artificial; the frame 

 of space comes into our minds with our first perception of 

 space. Consider, for example, the more extreme case 

 when the FitzGerald contraction is one-half. If a man 

 takes a rectangle 2"Xi" to be a square it is clear that 

 space must have dawned on his intelligence in a way very 

 different from that in which we have apprehended it. 



The frame of space used by an observer depends only 

 on his motion. Observers on different planets with the 

 same velocity (i.e. having zero relative velocity) will 

 agree as to the location of the objects of the universe; 

 but observers on planets with different velocities have 

 different frames of location. You may ask, How can 

 I be so confident as to the way in which these imaginary 

 beings will interpret their observations? If that objec- 

 tion is pressed I shall not defend myself; but those who 

 dislike my imaginary beings must face the alternative 

 of following the argument with mathematical symbols. 

 Our purpose has been to express in a conveniently 

 apprehensible form certain results which follow from 

 terrestrial experiments and calculations as to the effect 

 of motion on electrical, optical and metrical phenomena. 

 So much careful work has been done on this subject 

 that science is in a position to state what will be the 

 consequence of making measurements with instruments 



