176 STUDIES IN ELECTRO-PHYSIOLOGY; 



third force be adjusted so that O remains in its original 

 position, and suppose the weight to represent a force of 

 1 Ib. Then O is under the influence of three forces ; but it 



Fig. 93. 



is at rest, so that the forces are in equilibrium. The forces 

 OA and OB are both tending to draw O upwards, and they 

 are completely counterbalanced by the 1 Ib. weight. To 

 put it another way, the weight is tending to pull O down- 

 wards, but is counterbalanced by OA and OB. But the 

 weight would be counterbalanced exactly by a force of 

 1 Ib. acting in the direction directly opposed to it, that is, 

 in the direction of the straight line drawn up from O. If, 

 therefore, OA and OB be withdrawn, and one force sub- 

 stituted equal to the weight opposing them, equilibrium 

 will still be maintained. So the two forces OA and OB 

 can be replaced by a single force, which is called the resultant 

 force. If a parallelogram be constructed on OB, OA, as 

 indicated in the following figure, it will be seen that the 



Fig. 94. 



resultant force is the diagonal of the parallelogram. The 

 two forces OA, OB, are acting on a particle. To find the 



