1-26 



DRAWING INSTRUMENTS. 



Mr Bra- 

 nd'* com- 



PLAT* 

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Bow torn- 



adjusting it accurately to the divisions marked upon 

 th leg*. This contrivance is very useful, when the 

 coirtpjisaes are employed to make calculation* l>y means 

 of a plain scale . irts, but it in not requisite lor 



tlu- ordinary purposes of drawing. 



Drawing comjwsses tor describing circles, are of se- 

 veral kinds ; hut in general they have |x>ints, which 

 can be changed to draw either in pencil or ink. Fig. S. 

 is a pair of compasses, which are the invention of Mr 

 Brunei, and we think Hum letter adapted for general 

 purposes than any others we have seen. The I 

 shanks consist of two tubes A, B, united by the joint at 

 {'. the opening of which determine* the distance be- 

 tween the points of the legs a e and hf. These legs are 

 not attached immediately to the tubes A, B; but. by the 

 intervention of joints c, <l, the points can, in all situa- 

 tions, beset perpendicular to tin- paper, or nearly so, 

 without which the pen cannot draw a fair line, nor ran 

 an accurate measure lx- taken between the points. Be- 

 neath the joints c, d are a second pair, formed by a steel 

 pin g, fixed into the legs, and fitted through the joint- 

 pieces c, rf. These joint* bend in a direction perpendi- 

 cular to the upper ones, and are for the purposes of 

 changing the drawing points by inverting the legs, each 

 of which has at one end a plain steel point, marked (> 

 and e for measuring, or for a centre point ; and at the 

 oppo-ite ends, one has a port crayon f. and the other is 

 furnished with a steel pen a. This forms a complete 

 pair of measuring and drawing compasses, without any 

 loose parts, whieh are liable to be mislaid, and occasion 

 inconvenience to change them ; for in these the points 

 are changed instantly. Thus, in the Figure, they are 

 in a state to draw circles with the pen a; but, by turn- 

 ing the leg a e half round, on the joint pin c, the plain 

 measuring point e is brought into use for taking dis- 

 tances; or by bending the joints r, d, so that the points 

 are directed towards each other, they become well 

 adapted for callipering any circular bodies. For draw- 

 ing circles in pencil, the leg A /"must be inverted. The 

 joints g, are screwed up tight, so that they move ra- 

 ther stifly, and are not therefore liable to alter by the 

 action of drawing, though they are readily turned to 

 change the points. The tubes A, B are double, that is, 

 ach contains another smaller tube fitted within it; and 

 thejoint-pieces c,d, being attached to the internal tubes, 

 whilst the parts of the principal joint c are fixed to the 

 external tubes, the compasses can be greatly enlarged 

 by drawing out the tubes in the manner of telescopes. 

 They must of course be very accurately fitted into each 

 other, and have sufficient friction to preserve the situa- 

 tion to which they are drawn out. When drawn out to 

 the full extent, these compasses will describe a circle two 

 feet four inches diameter, or twenty inches in diameter 

 without extending the tubes, although the real size of 

 the instrument is very little more than double that of 

 the Figure. This great power is obtained by the legs 

 having joints to set them perpendicular ; and the tubes 

 may therefore be brought into a straight line with each 

 other, and the compasses act as well as before. The 

 tubes are extremely light, and nearly as strong as solid 

 one ; on the whole, we can recommend them as the 

 best instrument we have seen for general purposes, at 

 least for large circN 



The bow compasses must be used for smaller sized 

 circle- than the others will Conveniently draw. A very 

 capital pair of these is shewn in Fig. 3. of nearly their 

 real size. They have solid shanks and joints at r, d to 

 place the points perpendicular The points themselves 

 are moveable, being fitted into sockets, and held fast by 



rewsg, . This admits of changing cither of them. 

 The plain point tor measuring is shewn ;.t It, mid the 

 jxirt crayon, or pencil leg at S, and also a dotting wheel 

 leg at /. I -'ig. '). It- structure has l-en bct'ore de-cri- 

 iM'd. linv. always provided with a handle 1) 



at the top, which is fixed upon the joint, and i- 

 useful to turn the compasses round ..- < H they 



require to be moved for drawing \ery minute circles. 

 A duplicate pen-leg is frequently provided for this in- 

 strument ; and both pens being lived at once, it will 

 draw double lines at any required distance asunder, a 

 property which is very useful to surveyors tor drawing 

 roads in maps. By fixing the dotting leg and the pen 

 leg at once, the roads may be drawn with a dotted 

 line at one side. Some artists prefer having two sepa- 

 rate pair of bow compasses ; one for a pen, and another 

 for the pencil; they do not then fore require the soi k< t 

 joints i_..ff, which, for very nice purposes, are rather ob- 

 jrctionahlc ; for unless the sockets are extremely well 

 fitted, the points will not meet sufficiently near to draw 

 the smallest circles; still a pair of these, when in good 

 order, may be made to describe circles of only one 

 thirtieth of an inch in diameter. 



Pocket compasses of the best kind are shewn in Fig. 

 7. The shanks AB are made hollow for the reception 

 of the upper part of the legs, whieh separate at the 

 joints f,f. The legs have joints c, d to set them perpen- 

 dicular. One of the legs is shewn detached to explain 

 it, exhibiting the plain point at one end, and the port 

 crayon at the other. It has two parts at / and m, each 

 formed to fit into the sockets or end of the tube forming 

 the shank of the compasses. This admits of either point 

 being brought into use, for either end of the leg may 

 be introduced into the hollow of the shank, and then 

 the opposite end will be in use. The parts /, m must be 

 accurately fitted into the sockets, and must be at equal 

 distances from the jwints, otherwise the points will not 

 be of corresponding length when changed. The leg n 

 with the steel pen has likewise a plain point at the 

 other end, which is concealed within the hollow of the 

 shank A. The fitting of the parts / and m consist of a 

 round pin accurately fitted into the sockets at the ends 

 of the tubes, and with a small steel feather or fillet fix- 

 ed, projecting from one side of the pin, and received into 

 a corresponding notch in the side of the tube. The 

 great convenience of these compasses is their portabili- 

 ty, for the points or legs being put into a sheath or 

 thimble, they can be carried in the pocket without 

 any other case, and contain a very good set of instru- 

 ments in themselves, which an artist may at all times 

 carry about with him. The only objection to them is, 

 that if they are much used, the sockets wear, and the 

 legs will then have a shake or looseness, which must of 

 course be destructive of all accuracy, in either drawing 

 circles or measuring distances ; neither can the points 

 be changed so readily as those of Mr Brunei's, Fig. 8. 

 which are merely inverted. 



We have now described all the jointed compasses 

 which we think particularly worthy of notice ; for 

 though a number of different constructions besides these 

 are in constant use among artists, they are not so per- 

 fect as the above. Compasses require exceeding good 

 workmanship, particularly in the joints. The p. 

 these should be always composed of two different me- 

 tals, and are best made by soldering or brazing two 

 thin plates of steel to one leg, and fitting them into cor- 

 re-ponding openings or clefts cut in the metal com- 

 posing the other leg, which is generally brass or silver. 

 The centre pin should be rteel, and accurately fitted 



Or- 



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