Se ee ae ee ee 
Eee ee a a ee ee 
together by the tevacity of the parts of the inward. 
there may be abundance of {mall flaws or cracks, which , 
_ Glafs to a loofer an 
MicrocRaPHtayv) 49 
the Oven over the Furnace, do thereby C being made of; white, Glaf, 
which cools much quicker then green Glafs, and. is thereby’ made-much 
brittler_) acquire a very porous and. very brittle texture: fothat.ifwith - 
the point of a Needle or Bodkin,| the infide of any’ of them be rubbed 
prety hard, and thenlaid ona Table, it will, within a very little while, 
break into many pieces, with a brisk: noife, and throw the parts above a — 
{pan afunder on the Table: Now. though the pieces/are : not fo, fmallas 
thofe of a fulminating drop, yet they as plainly thew, that the outward 
parts of the Glafs have a great Cozatus to fly obiotier were they notheld | 
Surface : for we fee 
as foon as thofe parts are crazed by hard rubbing, and thereby their tena- 
city {poiled, the {pringinefs of the more outward. parts quickly makesa 
divulfion, and the broken pieces will, if the concave Surrice of them be 
further {cratcht with a Diamond, fly againinto fmaller pieces.; )jo. 0) 
From which preceding confiderations it will follow Sixthly 5, That the 
fudden flying afunder of the parts as foon as this Arch is any where difor- 
dered or broken, proceeds from the fpringing of the parts; which ,indea- | 
vouring to extricate themfelves as foonas they get the liberty , they per- | 
form it with fuch a quicknefs,that they throw one another away with very 
great-violence - forthe Particles that. compofe the Cruft havea \Comatus 
to lye further from one another, and therefore as foon as the external parts 
are locfened they dart themfelves outward with'great violence, juft as fo 
many Springs would do, if they were detained and faftened to the body, 
as foonas they fhould be fuddenly loofened; and the internal - 
ing inward, they contract fo violently, that they rebound back again anc 
fly into multitude of {mall fhivers or fands. Now though they appear 
not, either to the naked Eye, or the Aéicrofcope, yet lam very apt to think 
: by reafon the 
{trong reflecting Air is not got between the: cotiguous parts, appear not. 
And that this may be fo, |] argue from this ; that I have very ches een 
able to makeva crack or flaw, in fome convenient pieces of Glals,to aRpese 
and difappear at pleafure,, according as by prefling together, . or pulling 
afunder the contiguous parts, Iexcluded or admitted the {trong reflect- 
ing Air between the parts:. And it is very, probable, that there may be 
fome Body, that is cither very rarified Air, or fomething azalogoxs to it, 
which fills the bubbles of thefe drops ; which I argue, firft, from the round+ 
nefs of them, and next, fromthe vivid reflection of Light which they, ex- 
hibite : Now though [doubt not , but that the Air in them is very, much 
rarified,yct that there is {ome in them, to fuchas well confider this Expe- 
riment of the difappearing of a crack upon the extruding of the Air, I 
fuppofe it will feem more then probable. pees hog 
, The Seventh and laft sath Sek that I fhall proye,is, That the gradual 
heating and cooling o thefe fo extended bodies does reduce the parts of the 
2 ise temper. And this I found by heating them,,and 
keeping them for a prety while very red hot in a fire; for thereby L found 
them to growa little lighter, and the {mall Stems to be very ¢alily, bro- 
ken and inapt any where , without. at all making the drop fly ;, wherea 
; Sores ee '. before 
4a é 5 7 s fared ; 
