282 Mr HARRIS'S Experimental Inquiries concerning 



cylinder x : it is closed at each end, but has a small hook screw- 

 ed into the upper part, which can be occasionally removed, so as 

 to load the interior with as much weight as shall make it exactly 

 equal to the weight of the iron or magnet a?, when weighed in 

 an accurate balance. The machine, with the iron #, thus put in 

 equilibrio, will be sufficiently delicate, if, when loaded with a 

 weight of 500 grains, about one-tenth part of a grain will set it 

 in motion. 



To retain the wheel a be, Fig. 1. in its situation at the time of 

 removing either of the suspended bodies, there is a small brass 

 prong, Fig. 4. occasionally inserted in two holes drilled through 

 the quadrant, so as to enclose the steel point b which carries the 

 index : thus the wheel cannot fall either to one side or the other. 



10. In order to regulate the distance at which an attractive or 

 repulsive force may be caused to operate on the body x, there is 

 an adjusting apparatus represented in Fig. 1. by means of which 

 a magnetic bar H, or a horizontal plane AB, Fig. 9. (PI. XI.), 

 may be elevated or depressed through any required space. 



It consists of a vertical screw ST, Fig. 1., eight inches in 

 length, which passes through a corresponding nut at s, resting 

 finally upon the metallic foot at T : this foot is secured to a cir- 

 cular base of a convenient size. The nut at * is fixed to a small 

 horizontal plane of brass, sy, an inch and three quarters in length, 

 and an inch wide : this plane is preserved in its position by the 

 guide Sh, which also assists in supporting the circular top S ; 

 there is a brass rod of about three-tenths of an inch in diameter, 

 and eight inches long, which passes freely through a small pro- 

 jecting ring at S, and is screwed beneath into the brass plane at 

 h f ; the use of this rod is to sustain the square band of brass V, 

 through which passes the magnet H and scale my. The band V 

 is united to the upper part of the brass-rod by a nut and screw 

 at r, and incloses a space an inch wide, eight-tenths of an inch 



