were so Superficial, that how little soever we scrap'd off the Surface of
the Lead, we did in such places scrape off all the Colour, and discover
only that which is natural to the Metall it self, which receiving its
adventitious Colours, only when the heat was very Intense, and in that part
which was expos'd to the comparatively very cold Air, (which by other
Experiments seems to abound with subtil Saline parts, perhaps not uncapable
of working upon Lead so dispos'd:) These things I say, together with my
observing that whatever parts of the so strongly melted Lead were expos'd a
while to the Air, turn'd into a kind of Scum or Litharge, how bright and
clean soever they appear'd before, suggested to me some Thoughts or
Ravings, which I have not now time to acquaint You with. One that did not
know me, _Pyrophilus_, would perchance think I endeavour'd to impose upon
You by relating this Experiment, which I have several times try'd, but the
Reason why the _Phænomena_ mention'd have not been taken notice of, may be,
that unless Lead be brought to a much higher degree of Fusion or Fluidity
than is usual, or than is indeed requisite to make it melt, the _Phænomena_
I mention'd will scarce at all disclose themselves; And we have also
observ'd that this successive appearing and vanishing of vivid Colours, was
wont to be impair'd or determin'd whilst the Metal expos'd to the Air
remain'd yet hotter than one would readily suspect. And one thing I must
further Note, of which I leave You to search after the Reason, namely, that
the same Colours did not always and regularly succeed one another, as is
usually in Steel, but in the diversify'd Order mention'd in this following
Note, which I was scarce able to write down, the succession of the Colours
was so very quick, whether that proceeded from the differing degrees of
Heat in the Lead expos'd to the cool Air, or from some other Reason, I
leave you to examine.

[_Blew, Yellow, Purple, Blew; Green, Purple, Blew, Yellow, Red; Purple,
Blew, Yellow and Blew, Yellow, Blew, Purple, Green mixt, Yellow, Red,