f 19 J 



It confifts of a circukr plate of glafs Ji, (made of a pic:c of 

 looking-glafs) whofe upper furface is plane and polifhed, but the 

 under furface has its poIilTi taken away by being rubbed with a 

 piece of lead and flour of emery with water, fo that an image of 

 any objetH: can appear by refledion from its upper furface only : 

 to this is cemented with black fealing-wax the frame B C, (made 

 of fteel, or it might be of brafs) both having been previoufly 

 made very clean and bright and heated in an oven, then cooled 

 llowly : this frame is compofed of the round plates B and C 

 fattened together by the two rods or pillars a a flrongly riveted 

 or brazed to both plates : the piece D E F is compofed of the 

 round plate D, which is exadly fitted and fcrewed clofe and im- 

 moveable by two fcrews to the plate C, fo that both may be 

 parallel to A and B. In the middle of the plate D is brazed 

 the pipe p p : this pipe is made of fteel, and its fides as thfn and 

 light as may be confiftent with ftrength to fecure it from being 

 eafily bent ; it tapers a little towards its end, and its mean ex- 

 ternal diameter is about -^ of an inch : in the middle of this pipe 

 is a fteel wire hardened towards the lower end and tapering up- 

 wards towards E, where it is fcrewed (loofely) through the middle 

 of a ftiort pin or plate fattened in the mouth of the pipe, which 

 pipe is (for ftrength) inferted quite through the plate D. The lower 

 end of the wire, which extends a little below the pipe, has a hole 

 through it at G at right angles to its axis, as reprefented (enlarged) 

 in fig. 4, and alfo in fig. 5 in another fedtion of the wire which 

 is at right angles to the fedlion in fig. 4: this hole is to contain the 



knot 



