The Natuke of Physical Keality 87 



and does not indicate the existence of anything 

 mysterious or incomprehensible in the ultimate 

 make-up of the universe. Algebraic symbols are 

 of significance only in so far as they represent 

 magnitudes which can be measured, and all mea- 

 surements have space and time as their back- 

 ground. It is generally conceded that space is 

 perfectly symmetrical, and it has recently been 

 shown by G. N. Lewis that time is also symmet- 

 rical with respect to past and future. It should 

 therefore be entirely possible, and would appear 

 to be perfectly logical, to represent the phenomena 

 of nature by a system of mathematics which is 

 symmetrical in the use of positive and negative 

 signs. Such a system would contain no imaginary 

 quantities, but would not lend itself as readily for 

 the solution of equations as our present system. 



The special principle of relativity which com- 

 prises the incomprehensible proposition that the 

 velocity of light is independent of the relative 

 velocity of observer and source has been proposed 

 in an effort to explain the negative result of 

 the Michelson-Morley experiment. It has been 

 shown, however, that the results of this experi- 

 ment can be completely accounted for if we as- 

 sume that the light waves, after leaving a source 

 which moves along with uniform velocity, re- 



