DYNAMICS. gl 



ment or comparison of its parts, is called Absolute 

 Time : when subjected to measurement or reckon- 

 ing of any kind, it is called Relative Time. 



The least portion of time that we can measure is 

 about one-fourth or one-fifth of a second ; yet, were 

 we to trace the progress of nature minutely, a hun- 

 dred or even a thousandth part of a second would be 

 found to be distinguished by great changes. 



49- The velocity of a moving body, or the rate 

 of its motion, is said to be uniform, when the lines 

 it passes over (or, as it is usually expressed, the 

 spaces it describes) in equal times, are all equal to 

 one another. 



a. In measuring the velocities of bodies, it is conve- 

 nient to take a certain portion of time for the unit, 

 in terms of which all other portions of time are to 

 be expressed. The unit here assumed is one se- 

 cond. 



50. The space which a body moving with a uni- 

 form velocity passes over in any time, is had by 

 multiplying the time into the velocity, that is, by 

 multiplying the number of seconds the motion has 

 continued into the space moved over in one se- 

 cond. 



a. Hence if S be the space passed over in the time T, 

 with the uniform velocity V, (all of them being ex- 

 pressed numerically), 



S = V x T. 



51. In 



