158 Mr PocMington, Units of M ass, Length and Time. 
in these units is 3 0 x 10 5 , the constant is r3y -6 , and again we 
have a number, T3, which is near to unity. 
10. General conclusion. There are four fundamental qualities 
of the ether, hence no theory of the ether and matter can explain 
all the facts unless it involves four such qualities. The granular 
theory of Reynolds* is as far as I know the only one that satisfies 
this condition. (The four qualities may be represented by the 
radius of a grain, its mean velocity, its mass, and the pressure in 
the medium at infinity, or we may of course choose our four 
quantities in other ways.) We can in four ways choose our units 
of length, mass and time so as to reduce three out of four of the 
numbers expressing these qualities to unity. , One such set of 
units has been found in § 9. 
* Osborne Reynolds, Papers on Mechanical and Physical Subjects, Yol. iii. ‘The 
Submechanics of the Universe.’ 
