MICROSCOPIC DRAWING AND ENGRAVING. 
lines composing* a band, which a power of 2000 would barely 
render visible to average eyes. Assuming that such eyes could 
see distinctly without microscopic aid the lines of a band consisting 
of 150 to an inch, it is evident that a power of 2000 would render 
equally visible those of a band, the lines of which would be 300000 
to an inch. I am not aware that Mr. Nobert, or any other artist, 
has ever produced such lines, and consequently doubt the existence 
of any such artificial test for a power of 2000. 
31. I now come to notice a sort of microscopic engraving, which, 
though it is at once the most curious and difficult, has not, so far 
as I am informed, had as yet any directly useful application. 
Regarded, however, as an example of mechanical ingenuity and 
skill, and as an artistic tour de force of the highest order, it is 
full of interest. 
However much we may admire the production of the micrometric 
scales and microscopic test-plates described above, there is nothing 
in them to excite surprise, save the precision which is combined 
with such extreme minuteness. To draw a series of parallel lines 
of regulated length and uniform intervals, is a problem, to the 
solution of which it is easy to conceive that finely constructed 
mechanism can be adapted; but when it is proposed to delineate 
objects and characters, in which no such regularity prevails, and, in 
tracing which, the point of the graving tool must pursue a course 
determined by conditions, which obviously cannot be represented 
by any kind of mechanism, and to accom¬ 
plish which it must be guided, directly or 
indirectly, by the hand, a problem of quite 
another, and far more difficult order, is 
£ presented: such, however, is the curious 
and complicated problem for which Mr. 
j- Froment, already named, has found a 
solution. 
This eminent artist has succeeded in 
A producing manuscripts and drawings, en¬ 
graved upon glass, on a scale of minuteness 
L in no degree less surprising, though far 
40 more difficult of execution than the test- 
plates; of Mr. Nobert. 
^ To enable the reader more easily to 
appreciate these wonderful productions, we 
have given in fig. 25 the forms and magni¬ 
tudes of five small circular spaces, A, b, c, d, 
e, the diameters of which are severally the 6th, 12th, 30th, 70th, 
and 160th of an inch. 
Mr. Froment Wrote for me, in less than five minutes, within a 
Fig. 25 . 
