2 >N. 



the force, that is. tlio direction in which it tends to make 

 the particle s* 1 the intensity >f the force. As the 



dimensions of a particle finitely small its position 



may be determined in tin- >am- manner as that of a point 

 in geometry, and the direction of the for < deten 



in the same manner us that of a straight line in 



proceed then to consider the magnitude or intensity of 

 a force. 



7. Forces can be measured by taking some force as th 

 unit, and expressing by numbers the ratios which other f 

 bear to this unit. Two forces are equal win n ! in 

 in opposit- ns to a particle they maintain equilibrium. 



take two equal forces and apply them to a particle in the 

 same direction we obtain a fom of either ; if we unite 



three equal forces we obtain a trijili force; and so on. 



AVhen we say then that a force applied to a particle 

 certain multiple of another force, we mean that the first force 

 1*5 supposed to be compos- i tain number of forces 



equal to the second and all acting in the same direction. In 

 this way forces become measurable quantities, which can be 

 expressed by numbers, like all other quantities, by 

 them to a unit of their own kind. Forces may also be r 

 sented by straight lines proportional in length to these num- 

 bers, drawn from the point at which the forces act aud in the 

 directions in which they act. 



8. Experience teaches us that if a body be let free from 

 the hand, it will fall downwards in a certain di. bow- 



irequcntly tl. iinent be made, the result is th<> 



same, the body strikes the same spot on the ground in 



vidcd the place from which it is dropp u the 



. The cause of this und to be 



an affinity which all bodies have for the earth, and is t< : 

 the force of attraction. If the body be prcvntr 1 from 1 

 .e interposition of a table or of the hand, the body e 

 * pressure on the table or hand. \\', i.jld is the nam 

 the pressure which the attraction of the earth causes a body to 

 on another with which it is in contact. 



