for drawing in PerfyeBm* 369 
fentation of the place and pofition of the line may be then 
drawn upon the paper, by the top edge of the ruler ST, a trifle 
longer at each extremity than it appears to be. This operation 
may be repeated for as many lines as can be obtained in the 
firft pofition of the papered board and parallelogram ; when they 
muft be fhifted into the other recefs and groove, to find the reft, 
which may be now done without taking any further notice of 
the divifions on the rulers. 
N. B. A common T fquare, applied to a board of this kind, 
will anfwer molt purpofes. For example * place the flock of 
fuch a fiquare in one of the grooves, having a blade not lefs 
than the length HK or HR ; mark the fpaces HI and QR 
upon the upper edge thereof, and divide each of them into any 
convenient number of equal parts, and figure the faid parts in 
the ufual manner, to correspond with each other, as may be 
feen in fig. 1. Now, fuppofe the flock of the fquare to be in 
ED, it is plain, that all perpendicular lines may be drawn 
upon the paper KLMM in their proper places, and (by means 
of the divifions on the edge of the fquare) neaily of (though 
properly a trifle more than) their true length. All the lines of 
this defcription being obtained, the fluffing board mufl be 
placed in its other recefs, and the flock of the fquare into the 
other groove ; then, beginning with the firft line, bring the 
edge of the fquare to agree with its limits, and mark them off 
upon the line on the paper, and fo of all the reft in fueceflion 1 
and join the paints, where neceflary, with a common ruler. 
■FIG. III. (t ab. XIV.) 
This apparatus is contrived to avoid the trouble of contF . 
finally working againft a board in a vertical pofition. In order 
C c c a to 
