31 ft On ftriking Fire with a Flint and Steel. 
Hook examined feveral of them with a micro fcope, and 
found that a black particle, no bigger than a pin’s point, 
appeared like a ball of polifhed fteel, as at fig. 558. and 
ftrongly reflected the image of the window, and of a 
flick which he moved up and down between the light 
and it. Others were, as to their bulk, pretty round, 
but their furface not fo fmooth ; fome were cracked, as 
fig. 559. others broke in two, and hollow, as fig. 561. 
feveral others were found of other fhapes ; but that re- 
prefented at fig. 560. was obferved to be a big fpark of 
fire, and ftuck to the flint, by the root F, at the end of 
which Hem was fattened an hemifphere, or hollow ball. 
It is alfo remarkable, that fome of thefe fparks are flivers, 
or chips of iron vitrified, others are only the flivers melted 
into balls, without vitrification n , and the third kind are 
only finall flivers of the iron, made red-hot with the 
violence of the ftroke given on the fteel by the flint. 
Many forts of fand, fome gathered on the fea-fhore, 
or on the fides of rivers, and fome found on the land, 
differ irv the fize, form, and colour of their grains, fome' 
being tranfparent, others opake, fome have rough, and 
others quite fmooth furfaces. It would be endlefs to de¬ 
scribe all the figures to be met with in thefe kind of mi¬ 
nute bodies, they being fpherical, oval, pyramidal, co¬ 
nical, prifmatical, &c. Mr. Hook trying feveral magni¬ 
fying glaffes, by viewing a parcel of white fand, cafually 
hit upon one of the grains, which was exactly fhaped and 
wreathed like a Shell, which he feparated from the reft 
of the granules, and found it to appear to the naked eye 
no bigger than a pin’s point, but when viewed in the 
microfcope, it appeared as in fig. 562. refembling the 
Shell of a fmall water fnail 0 3 it had twelve wreathings, 
growing all proportionably one lefs than the other, to¬ 
wards 
n Hook’s Mic. p. 44. f Ibid. p. 80. 
