1 28 The Diacatoptron. 



h.ind directine: the pencil, and the object to be traced, may 

 be equally well defined and clear. Another advantage pos- 

 sessed by this ajjparatus is, that very lilile light is lost, as is 

 the case where many glasses intervene between the object 

 and its representation. The application is also iraniediaiely 

 obvious to the most careless observer. 



Take a perRclly clear piece ol' glass, a foot, square, well po- 

 lished aiid quite even, and parallel throughout ; place this in 

 a t'raine (PI. III. fig. 1.) about one inch and a halt' wide, and 

 one inch thick, and instead oF wood ai the bottom ot the 

 frame place a brass wire or narrow and thin plate whicii 

 will hold the three side;? together, and prevent the glass 

 from falling out, as it must rest on the wire or plaie, which 

 siionld be fastened tight to the feet of the fraine. 



The feet must be cxactlv at right angles' with the frame, 

 so that when the plate is placed upon an even table, it v\ill 

 stand perpendicular. In the upper part of the irame at b, 

 make a Ions groove, in which insert the brass sight an inch 

 broad (fig. 70 having the small eye-hole c; this is to be 

 fastened at lop by the screw d, which may be screwed up 

 or loosened at pleasure. 



Divide the frame (fig. 5.) into two equal parts, beginning 

 at the upper part from the groove h, to the bottom of the 

 feet o, or of the brass wire. Divide again the lower part 

 j'rom e into eight equal parts, and on each side of the 

 frame bore holes, taking great care to place thein exactly at 

 the eight measured points. 



A board (fig. 6.) is called the table, of the breadth of the 

 frame, in which two brass pins are fastened of such size 

 that ihey niav exactly pass into the holes to raise the table 

 to diiTerent heia;hts corresponding with the holes in the 

 frame ; otherwise you cannot magnify or diminish objects 

 correctly according to the size you may wish to obtain. 

 Oii the opjiosite side of the table are supports at each cor- 

 i5er, so pU;ced that they may be conveniently pushed up or 

 down. The supports pass through two holes in the talde, 

 and in each are eight small holes of the same size as those 

 in the frame, so that by means of a brass wire under the 

 table it may be kept fast in a horizontal position. 



The blind (fig. 2.) ismade ofa piece of wood, bevelled, one 

 foot lonsj <Hie inch and a half wide, and one inch in thick- 

 ness. A brass or iron rod is bent in such a manner as 

 to form a stjuare, and the wood serves as a support to it. 

 This frame is then covered with writing paper, which sho;dd 

 be of moderate thickness. When you make use of the 

 apparatus, place the object A upon a flat table on a level 



with 



