PEN 



PEN 



which is to be copied; or a crayon to 

 draw the figure, or copy of the original 

 design ; these three points must be al- 

 ways in one right line, and by the con- 

 struction of the levers,- if they are once 

 set in a line, they will continue in it 

 through any of its motions. 



The proportion in which it will reduce 

 any figure will be easily calculated from 

 the same principles as the lever ; that the 

 magnitude of the figures described by 

 either of the points, will be in the same 

 proportion to each other, as the distances 

 of those points from the fulcrum, thus if 

 the point/ be the fulcrum, and if the dis- 

 tance from f to g be half the distance 

 from /to A, the size of the figure describ- 

 ed by the point will be half the size of 

 the figure described at the same time by 

 the point h. The fulcrum, as we have 

 said before, can be changed, as also the 

 pencil and the tracer, and any of the three 

 can be applied to either of the tubes upon 

 the levers, if the tracer is placed in the 

 tube /i, the pencil in g, and the fulcrum at 

 /, any figure described by the tracer h, 

 will be exactly copied one half the size 

 by the pencil at^, and if on the conti-ary 

 the pencil is placed at h, and the tracer at 

 , the figure drawn by the pencil will be 

 twice the size of the original traced at g. 



When the fulcrum is placed between 

 the two points at^, the figures described 

 by each point will be inverted with re- 

 spect to each other, though the same 

 principle applies, that the magnitude of 

 the figures will bear the same proportion 

 to each other, as the distances of their 

 tracing point from the fulcrum bear to 

 each other. This last position of the in- 

 strument is seldom used on account of the 

 figure being inverted, except when the 

 figures traced and copied are equal to 

 each other, or nearly so, as the first posi- 

 tion will not allow of that. 



It will be easily seen that by the sliding 

 motion of the tubes, g and/, the propor- 

 tion between the three may be varied in 

 any degree, and for this purpose the le- 

 vers are engraved, and divisions made to 

 set the tubes by, so as to reduce it in any 

 proportion, and at the same time put the 

 three points in the same right line, other- 

 wise the figures will be strangely distort- 

 ed ; n n n is a silk thread, which the ope- 

 rator hooks round his fore finger, by pull- 

 ing this he raises up the crayon, g, so that 

 it will not mark ; each joint of the instru- 

 ment is formed by a short axis, i, (fig. 2), 

 made fast and moving with one lever, k, 

 it has pivots at its ends, working in a small 

 cock, /, screwed to the upper side of the 



other lever : beneath each joint a small 

 tube, in, is screwed, its upper end re- 

 ceives the lower pivot of the axis i, and 

 in the lower part a small spindle, ?i, is 

 fitted, which has a castor at the bottom 

 to support the weight of the instrument, 

 by the turning of the spindle, ??., the cas- 

 tor will run in any direction. One of 

 these castors is also fixed at the outer end 

 of the levers, A and B, as well as beneath 

 each joint. Care should be taken that 

 the table, upon which the instrument is 

 used, is a perfect plane, otherwise errors 

 will arise from the tracer or crayon being 

 sometimes thrown out of the perpendicu- 

 lar, and it is for the same reason that the 

 levers are jointed with an axis, as explain- 

 ed before. 



Fig. 4, Plate Pentagraph, is the com- 

 mon parallel ruler, A B are two rulers 

 connected by two bars C D, which are of 

 equal lengths, and the distance between 

 the pins by which the levers C D are fixed 

 to the rulers are the same distance from 

 each other in both rulers ; by this means 

 it is easily seen, that the two rulers, A B, 

 will always move parallel to each other. 



Fig. 5. is another ruler differing from 

 the other in being double ; the advantage 

 of it over fig. 4, is, that the two rulers 

 A B can be moved parallel to each other 

 without sliding endways, as the other 

 does, every part of the moving ruler de- 

 scribing the arc of a circle. 



PENTAMETER* in ancient poetry, a 

 kind of verse consisting of five feet, or 

 metres ; whence the name. The two 

 first feet may be either dactyls or spon- 

 dees, at pleasure; the third is always a 

 spondee, and the, two last anapests : such 

 is the following verse of Ovid. 



123 4 5 



Carmini\bus vi\ ves tern \pns in o \ mne meis. 



A pentameter verse, subjoined to an 

 hexameter, constitutes what is called 

 elegiac. 



PENTANDRIA, in botany, the name 

 of the fifth class of plants in the Linnaean 

 system, consisting of plants which have 

 hermaphrodite flowers with five stamina. 

 There are six orders in this class, found- 

 ed upon the number of styles. 



PENTAPETES, in botany, a genus of 

 the Monadelphia Dodecandria class and 

 order. Natural order of Columniferae. 

 Malvacese, Jussieu. Essential character: 

 calyx double, outer three-leaved ; inner 

 five -parted ; stamina fifteen, with five 

 ligules, petal shaped ; capsule five-celled, 

 many-seeded. There is but one species, 



