The sharpest _Edge_ hath the same kind of affinity to the sharpest _Point_
in Physicks, as a _line_ hath to a _point_ in Mathematicks; and therefore
the Treaty concerning this, may very properly be annexed to the former. A
Razor doth appear to be a Body of a very neat and curious aspect, till more
closely viewed by the _Microscope_, and there we may observe its very Edge
to be of all kind of shapes, except what it should be. For examining that
of a very sharp one, I could not find that any part of it had any thing of
sharpness in it; but it appeared a rough surface of a very considerable
bredth from side to side, the narrowest part not seeming thinner then the
back of a pretty thick Knife. Nor is’t likely that it should appear any
otherwise, since as we just now shew’d that a _point_ appear’d a _circle_,
’tis rational a _line_ should be a _parallelogram_.
Now for the drawing this second Figure[3] (which represents a part of the
Edge about half a quarter of an inch long of a Razor well set) I so plac’d
it between the Object-glass & the light, that there appear’d a reflection
from the very Edge, represented by the white line abcdef. In which you may
perceive it to be somewhat sharper then elsewhere about d, to be indented
or pitted about b, to be broader and thicker about c, and unequal and
rugged about e, and pretty even between ab and ef. Nor was that part of the
Edge ghik so smooth as one would imagine so smooth bodies as a Hone and Oyl
should leave it; for besides those multitudes of scratches, which appear to
have raz’d the surface ghik, and to cross each other every way which are
not half of them exprest in the Figure, there were several great and deep
scratches, or furrows, such as gh and ik, which made the surface yet more
rugged, caus’d perhaps by some small Dust casually falling on the Hone, or
some harder or more flinty part of the Hone it self. The other part of the
Razor ll, which is polish’d on a grinding-stone, appear’d much rougher then
the other, looking almost like a plow’d field, with many parallels, ridges,
and furrows, and a cloddy, as ’twere, or an uneven surface: nor shall we
wonder at the roughnesses of those surfaces, since even in the most curious
wrought Glasses for _Microscopes_, and other Optical uses, I have, when the
Sun has shone well on them, discover’d their surface to be variously raz’d
or scratched, and to consist of an infinite of small broken surfaces, which
reflect the light of very various and differing colours. And indeed it
seems impossible by Art to cut the surface of any hard and brittle body
smooth, since _Putte_, or even the most curious _Powder_ that can be made
use of, to polish such a body, must consist of little hard rough particles,
and each of them must cut its way, and consequently leave some kind of
gutter or furrow behind it. And though Nature does seem to do it very
readily in all kinds of fluid bodies, yet perhaps future observators may
discover even these also rugged; it being very probable, as I elsewhere
shew, that fluid bodies are made up of small solid particles variously and
strongly mov’d, and may find reason to think there is scarce a surface _in
rerum naturâ_ perfectly smooth. The black spot mn, I ghess to be some small
speck of rust, for that I have oft observ’d to be the manner of the working
of Corrosive Juyces. To conclude, this Edge and piece of a Razor, if it had
been really such as it appear’d through the _Microscope_, would scarcely
have serv’d to cleave wood, much less to have cut off the hair of beards,
unless it were after the manner that _Lucian_ merrily relates _Charon_ to
have made use of, when with a Carpenters Axe he chop’d off the beard of a
sage Philosopher, whose gravity he very cautiously fear’d would indanger
the oversetting of his Wherry.
* * * * *