ELECTRICAL UNITS OF MEASUREMENT. 103 



and grammes may be as much a thing of the past 

 as grains are now. 



There is something exceedingly interesting in 

 seeing that we can practically found a metrical 

 system on a unit of length and a unit of time. 

 There is nothing new in it, since it has been 

 known from the time of Newton, but it is still a 

 subject full of fresh interest. The very thought 

 of such a thing is full of many lessons in science 

 that have scarcely yet been realised, especially as 

 to the ultimate properties of matter. The gramme, 

 it will be remembered, is founded on the proper- 

 ties of a certain body, namely, water ; but here, 

 without invoking any particular kind of matter, 

 simply choosing a certain definite length marked 

 on a measuring rod, and a unit of time (how 

 obtained, we shall consider presently), we can 

 take up a piece of matter, and tell, in any part of 

 the universe, how to measure its mass in definite 

 absolute units. 



Think now of the two units on which this 

 universal-gravitation metrical system depends : the 

 unit of length and the unit of time. The unit of 



