257 
Perspective Drawing . 
drawn so as, by holding it up perpendicularly, we may 
see, and, as it were, render tangible, the truth of perspec- 
live lines of buildings; and for those whose sight is bad, 
or for very young people, it would not be amiss to take a 
copper-plate of the like dimensions, and with a fine nee- 
dle gently scratch out the like lines, in which case there 
will be no necessity to take off the burrs, as the engravers, 
call the ridges raised in ploughing copper; and from this 
plate, ten thousand impressions may be taken of the faint 
lines by way of guide, on the drawing-book of a young 
beginner, without injuring the plate ; for I can assure 
your readers, that it is more difficult to erase a slight 
scratch from a sharp needle on copper, by the act of tak- 
ing impressions, than the deepest cut of the graver; the 
reason of which is, that the ridges of the skin of the 
printer’s hand can never enter that fine line, whereas, in 
a coarse one, he polishes the edges of it down by every 
operation, and thus renders it a smooth channel, at last 
undefined, and incapable of retaining the printing ink; 
and the reason I am so diffuse on the subject is, that I 
think the knowledge of it may be generally useful, parti- 
cularly to those who wish to extend the publication of 
botanical outlines : as it is not necessary to be taught the 
art of engraving for those who can draw lines, to design 
on copper the peculiarities of plants, or their anatomy. 
How to trace deeper lines with certainty on copper as 
easily as on paper, I will have the pleasure to communi 
cate to you at my next leisure moment 
But, to return to our subject. 
To this simple contrivance, we may add a sheet of per- 
pendicular lines, by which means the uprights will all be 
shown ; and for very heavy intellects, at first even the 
horizontal scale might be useful, though I never found it 
so among my acquaintance. There are also many little 
helps of simple contrivances to further the first acquire- 
Vol. II. i 1 
