36 TWO NEW WORLDS 



electricity, it can be generated and destroyed. 

 Moreover, its amount can be expressed in terms 

 of the other fundamental quantities. Therefore 

 there is no necessity of regarding it as a funda- 

 mental quantity. 



All the quantities measured in mechanics and 

 physics are made up of measurements of one or 

 more of the four fundamental quantities : length L, 

 time T, mass M, and electricity E. Or if more 

 complex quantities are measured by direct reading, 

 as by a speed indicator or a thermometer, the result 

 is reducible to the four fundamental quantities. 



If, therefore, we wish to arrive at the mechanical 

 and physical constitution of any imaginable uni- 

 verse, we have only to ascertain how its fundamental 

 quantities compare with ours. 



Thus we might postulate a world in which all 

 masses and lengths are the same as in ours, but 

 in which everything happens ten times as fast. 

 Then it is easy to show that areas, volumes, angles, 

 densities, and moments of inertia are the same as 

 before. Acceleration, force, energy, and pressure are 

 multiplied a hundredfold, and power a thousand- 

 fold. Velocity and angular velocity are increased 

 ten times. But we shall be quite ignorant of any 

 change. For our times are measured by the earth's 

 rotation about its axis, or its revolution about the 

 sun, and the scale of measurement increases with 

 the quantity to be measured. 



