22 OUTLINES OF NATURAL PHILOSOPHY. 



51. In uniform motions, therefore, the velocity is 



S 

 equal to the space divided by the time, or V == ?- 



52. In uniform motions also, the time is equal 



S 

 to the space divided by the velocity, or T = -. 



In all these theorems T is expressed in seconds, and 

 V in some known measure of length, the same ia 

 which S is also expressed. 



53. The velocity of a body is sometimes estima- 

 ted in a direction different from that in which it ac- 

 tually moves. 



Thus, (fig. 1 .) if while a body B moves along the line 

 AC, a perpendicular BD be continually drawn to 

 the line AE, which makes with AC a given angle, 

 the velocity with which D moves along AE is called 

 the velocity of B in the direction AE. 



54. The velocity of a body moving in a given 

 direction, is to its velocity estimated in any other 

 direction, as radius to the cosine of the angle 

 which the two directions make with one another ; 

 or if V be the velocity of the body, j8 the angle 

 which the path of the body makes with another 

 line, V cos & is the velocity reduced to the direc- 

 tion of that line, 



If 



