

ELECTRICAL UNITS OF MEASUREMENT. 97 



units of length and time, on which to found the 

 units of force and mass. It is nevertheless inter- 

 esting, not only in respect to the ultimate 

 philosophy of metrical systems, but also as full 

 of suggestions regarding the properties of matter, 

 to work out in detail the idea of founding the 

 measurements of mass and force on no other 

 foundation than the measurement of length and 

 time. In doing so we immediately find that the 

 square of an angular velocity is the proper measure 

 of density or mass per unit-volume ; and that 

 the fourth power of a linear velocity is the proper 

 measure of a force. The first of these statements 

 is readily understood by referring to Clerk 

 Maxwell's suggestion, of taking the period of 

 revolution of a satellite revolving in a circle close 

 to the surface of a fixed globe of density equal 

 to the maximum density of water, as a funda- 

 mental unit for the reckoning of time. Modify 

 this by the independent adoption of a unit of time, 

 and we have in it the foundation of a measurement 

 of density, with the detail that the density of the 

 globe is equal to 3/(4?r) of the square of this 



H 



