436 Prof. Wallace on the Invention of the Pantograph, 



working. Fig. 3. shews the copying point, and its apparatus ; 

 P P is a black lead pencil, tt a tubular case into which the pen- 

 cil is fitted tightly : these, when the instrument is not used, are 

 detached from the arm and kept apart. The pencil-case has a 

 flanch y y, which surrounds it like a collar ; the part t of the case 

 above the flanch, may be called its neck : W, W, W, are round 

 discs of metal (three are shewn in the figure) ; each has a hole in 

 it, through which the neck of the pencil-case may be passed ; one 

 or more of these are placed on the neck when the instrument is 

 used, they serve by their weight to bring down the copying 

 point when raised in working, and also to give the proper degree 

 of shade to the pencil line traced on the paper. There is a bent 

 lever oj oc, the arms of which are nearly perpendicular to each 

 other. It is supported at its angle by the fulcrum s, which 

 stands on the arm of the instrument. The use of the lever is to 

 raise the copying point from the paper by lifting the pencil- 

 case in the tube T. For this purpose, there is a silk line 

 Imn H, Fig. 1. (of which Im, Fig. 3, is a part), fixed to it at / ; 

 this passes over the wheels of two small pulleys, one, m, support- 

 ed on the beam over the centre of the wheel, Fig. 1, and another, 

 n, fixed to the socket c, over its centre. The end H of the silk 

 line is held in the operator's left hand while he works ; by draw- 

 ing it he turns the lever about its centre. By this angular mo- 

 tion, the arm under the flanch raises the pencil in the tube ; by 

 slackening the line he allows it to descend, until its point again 

 reaches the paper. 



The pencil-case, when it is put into the tube T, does not 

 come into absolute contact with its inside, but is held firmly in 

 an upright position, by pressure on the convex surfaces of five 

 friction rollers which enter the tube, and project a little beyond 

 its inner surface. Two of these are at the top of the tube and 

 two at its bottom, directly under the former (only one of each 

 pair, viz. r' r", are seen in the figure) ; the fifth, r, is on the op- 

 posite side of the tube, towards the wheel, so that its pressure 

 may be opposed to that resulting from the combined pressure of 



