Opticks 1717 - Up

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.I-IElltd EXCeption. Now if compound Bodies
are fo w-y hard as we find fork Of them to
IX, and yet are verg porous, and confiit of Parts
which are only lard together ; the dimple Particles
which are void Of Pores, and were never
yet divided, n-~ufi be much harder. For fuclz
hard Particles being heaped rfp together, can.
fcarce touch one another in more than asfew
Points , and therefore muj% be .kparable by
lnuch MS Force than is requiiite to breal~ a iblid
Particle, whofe Parts touch in all the Space
between them, -\;rrichout any Pores or Interitices
to weaken their Cshefion. An,d how ‘fuch ve?
ry hard Particles which are ohly”laid together
and touch only in a few Points, can itick together,
and that fo firmly as they do, without the
aifiltance of fomething which caufes them to
bc attraAed or prefs’d towards one another, is
very diEicult to conceive.
The fame thing I infer alfo from the cohering
of two polifh’d .Marbles i;lz WWM, and from
the Standing of Quick-filver in the Barometer at
t-he height of 70, 60 or 70 ‘Inches, or above,
when ever it is well purged of Air and careful-
Ily po~md in, fo that its Parts be every where
contiguous both to one another and to the
Glafs. The &moQhere by its weight preik
the Quiclr-iilver into the Glafs, to the height of
29 or 30 Inches. And fame other Agent saifes
it higher, not by pre1ling it into the Glafs, bun.
by majiing its Parts iticlc to the Glnfs, and to’
one another. For upon any dikontinuation of
Parts, made eithqr. by Bubbles Or by fhakin the.
.8 MS*