OF SIMPLE ACCELERATING FORCES. 75 



therefore, be contented to acknowledge our total igno- 

 rance of the intimate nature of forces of every kind ; and 

 we have, at present, only to examine the effect of forces, 

 considered with regard to their magnitude and direction, 

 without inquiring into their origin. 



229, Defiistition. When the increase or 

 diminution of the velocity of a moving body 

 is uniform, its cause is called a uniform force; 

 the increments of space, which would be de- 

 scribed in any given time with the initial velo- 

 cities, being always equally increased or di- 

 minished. 



Scholium 1. The word velocity appears to be suffi- 

 ciently understood from common usage, although it is not 

 easy to give a correct definition of it. The velocity of a 

 body may be said to be the quantity or degree of its mo- 

 tion, independently of any consideration of its mass or 

 magnitude ; and it might always be measured by the space 

 described in a certain portion of time, for instance, a se- 

 cond, if there were no other motions than undisturbed or 

 uniform motions : but the velocity may vary very consi- 

 derably within the second, and we must, therefore, have 

 some other measure of it than the space actually described 

 in any finite interval of time. If, however, the times be 

 supposed infinitely short, the elements of space described 

 may be considered as the true measures of velocity. 

 These elements, though conceived to be smaller than any 

 assignable quantity, may yet be accurately compared with 

 each other; and the reason that they afford a true criterion 

 of the velocity is this, that the change produced in the 

 velocity, during an evanescent interval of time, must be 



