302 PHILOSOPHICAL TRANSACTIONS. [ANNO ]/82. 



pass clear of it, without danger of striking it; ancT also the arch mn is brought 

 so far forward as to leave no more than a clearance, sufficient for the rods to 

 vibrate freely without touching it. 



Fi^. 7, shows one of the compound bodies, drawn of a larger size, ab is a 

 block of wood, and about as much in breadth as it is represented in height, 

 through a hole in which the wooden rod cc passes, and is fixed in it. db repre- 

 sents a plate of lead, about ■§ of an inch thick, one on each side, screwed on by 

 way of giving it a competent weight, ibefg represents the edge of a springing 

 plate of brass, rendered elastic by hard hammering; it is about -§- of an inch in 

 breadth, and about ^ of an inch thick. It is fixed down on the wooden block 

 dB by means of a bridge plate, whose end is shown at hi, and is screwed down 

 on each side the spring plate by a screw which, being relaxed, the spring can be 

 taken out at pleasure, and adjusted to its proper situation, kl is a light thin slip 

 of a plate, whose under edge is cut into teeth like a fine saw or ratchet, and is at- 

 tached to the spring by a pin at k, which passes through it, and also through a 

 small stud rivelted into the back part of the spring, and on which pin, as a 

 centre, it is freely moveable. 



mn shows a small plate or stud seen edgeways, raised on the bridge plate, 

 through a hole in which stud the ratchet passes ; and the lower part of the hole 

 is cut to a tooth shaped properly to catch the teeth of the ratchet, and retain it 

 together with the spring at any degree to which it may be suddenly bent ; and 

 for this purpose it is kept bearing gently downward, by means of a wire-spring 

 opq, which is in reality double, the bearing part at o being semi-circular ; from 

 which branching off on each side the rod cc, passes to p, and fixes at each end 

 into the wood at q. However, to clear the ratchet, which is necessarily in the 

 middle as well as the rod, the latter is perforated ; and also the block is cut away, 

 so far as to set the main spring at e free of all obstacles that would prevent its 

 play from the point b. The part (g is shown thicker than the rest, by being 

 covered with thin kid leather tight sewed on, to prevent a certain jarring that 

 otherwise takes place on the meeting of the springs in collision. 



In tig. 6, the marks on the arch mn are put on as follows, op is an arch of a 

 circle from the centre 1, and qr an arch of a circle from the centre k intersecting 

 each other at s. Now the middle line of the marks t, v, are at the same dis- 

 tance from the middle line at s that the centres Ik are ; so that when each body 

 hangs in its own free position, without bearing against the other, the rodef will 

 cover the mark at t, and the rod gh will cover the mark at v. From the point 

 s and on the arches sp and sq respectively, set off points at an equal and com- 

 petent distance from s each way, which will give the middle of the mark w and 

 x: and on the arch sp find a middle point between the mark v and w, which let 

 be y ; and on the other side, in like manner, on the arch sq find a middle point 



