the Laws of Magnetic Forces. 281 



by a contrary and equal force, it may be considered as existing 

 in free space, devoid of weight, and it will therefore remain quies- 

 cent, until some new force be applied to it ; and thus the action 

 of the force we seek to investigate will become so far evident and 

 unimpeded by any obstacle arising from gravity, except the fric- 

 tion and inertia of the wheels, and the resistance of the air *, 

 which in this case need not be taken into account. 



Thus, if an attractive force cause the body #, Fig. 1., to de- 

 scend, then the index bl will move forward in the direction IN, 

 until a portion of the cylinder W drawn out of the water, ceases 

 to displace as much of the fluid as is equivalent to the force ap- 

 plied ; and thus we obtain a constant and known measure of the 

 new force, within a given range, which will be more or less ex- 

 tended, according to the dimensions of the cylindrical counter- 

 poise W, the intensity of the force, and the rate of its increase. 

 In like manner, if a repulsive force act on the body a? in a con- 

 trary direction to the former, then the index b I will move in the 

 direction IM, until a new portion of the cylinder W becomes 

 immersed in the water ; and thus an equivalent to the force of 

 repulsion is obtained in a converse way to the preceding. 



9. Previously to suspending the cylindrical counterpoise just 

 described (7.), the body x is to be put in equilibrio with an equal 

 and similar weight x', Fig. 1*, in order to observe, if when loaded 

 with the whole, the index is indifferent as to position on any 

 part of the arc, or nearly so, after carefully bringing it to rest. 

 (The weight of the silk, which is necessarily transferred from 

 one side to the other by the motion of the wheel, being consi- 

 dered of no value). For this purpose, there is a small hollow 

 cylinder of brass x', Fig. 1*, about the same dimensions as the 



* These weights being placed under the same circumstances as the weights in 

 the celebrated machine of Mr ATWOOD. See ATWOOD on Rectilinear Motion. 



