846 Prof. L. T. More on the Postulates and 



o£ ponderable bodies and can reduce their force and energy 

 to a problem of statical relations between actions and re- 

 actions, it is complete as a tbeor.j. And if further it can, 

 by an hypothesis which does not conflict with its own 

 deductions, link up with other phenomena in different 

 domains, it is a general theory; and this is exactly what the 

 classical mechanics is capable of doing. 



Einstein assumes that all measurements have equal im- 

 portance. That is not the case ; while it is true that 

 classical mechanics denies absolute position and motion, it 

 tacitly assumes that a coordinate system in a static relation 

 to the phenomenon is the ultimate system of reference. Let 

 us suppose that several persons observe the same phenomenon. 

 Obviously their conclusions as to positions and motions will 

 disagree, since each person must ultimately interpret the 

 phenomenon with reference to himself. Each observer 

 therefore chooses a frame of reference rigidly attached to 

 himself regarded as a point absolutely at rest. If A wishes 

 to compare his result with that of B, he must know also the 

 position and motion of B^s frame of reference with respect 

 to his own during the observation. Each person who 

 measures an action may apparently refer the action to a 

 coordinate system moving with reference to himself, but, he 

 must know the motion of the coordinate system and be able 

 to refer it to a coordinate system attached to himself. Nor 

 does Einstein escape this paradox. If all coordinate systems, 

 moving relatively to each other, are of equal importance, 

 then the world is a perfectly incomprehensible and fluctuating 

 affair. His method of introducing stability is to assume that 

 the velocity of light is an absolute constant of length per 

 unit time, to which all observers of a phenomenon may refer. 

 Thus two person's attempting to obtain concordant mea- 

 surements of a kinetic phenomenon may refer to the velocity of 

 light as a common and an invariable standard. And if either 

 attempts to derive a length standard from this velocity co- 

 ordinate, he will be forced to pin his system of coordinates 

 to a star so distant as to be fixed to all observers or else to 

 the absolutely stationary luminiferous aether, whatever that 

 may mean. 



This attempt to measure lengths by a velocity, even if it be 

 such a compliant standard as tlie velocity of light in vaaio or 

 aether, leads us into grave difficulties. In mechanics a length 

 is the distance between two points, and we derive from this 

 postulate that a velocity is the ratio of this distance and the 

 time taken by a body in traversing it. Einstein does -the 

 opposite ; the velocity of light is our standard measure; 



