[ 19 4 ] 
or Tenant T of the Lever A t B. It is pierced by 
fcvcral Holes, which anfwer to as many others on the 
Spur. Below this Mortife the Foot becomes more 
(lender and cylindrical; by this Part it enters into a 
round Hole in the Arm of the Chair; this (lender Part 
of the Foot is pierced by feveral Holes, in order to 
run an Iron Pin through, which lies flat on the Arm 
of the Chair, and keeps the Foot raifed to a Height 
proper for the Perfon that undergoes the Operation: 
For the greater Security one may run Two Pins 
through ; one which reds upon the Arm of the Chair, 
and the other on the Seat itfelf, through which the 
Foot pafles alfo. The Iron Foot, Fig. 3* may be pro- 
vided with a fort of large Ring C, under the Pin, 
which will render its Rotation the eafler. If one 
(hould prefer an Iron Foot, one may eaftly judge, that 
the Hole for it in the Arm of the Chair muft be made 
narrower, either by filling up the old one with an Iron 
Box or Clout, which may be taken away, if one will 
ufe a wooden Foot; or one may even at firft fit thofe 
Holes for the Iron Foot, fetting the wooden one quite 
afide. 
The Lever A> B , H, B , TAB. II. Fig. i . is the mod 
compound Piece of all, and withal the mod: important. 
It is made of a real Lever A, B , and of a Piece fitted 
to it B), G , TAB. II. and III. The Lever properly fo 
called A f By TAB. II. is made round on its inferior 
Surface; the upper Surface is flat, and all along on 
the Middle of it there runs a Rod, forked at the End, 
which fits to a Groove of the fame Figure in the inferior 
Surface of the Sliding-piece F,G, TAB. III. ThisLever 
grows lefs and lefs towards the Extremity A, where the 
moving Power is to be applied ; the other Extremity, 
