Of the nature of a certain Stone, found in the _Indies_ in the head of
a _Serpent_. Of the way, used in the _Mogol's_ Dominions, to make
_Salt-petre_. An Account of _Hevelius_ his _Prodromus Cometicus_, and
of some Animadversions made upon it by a _French_ Philosopher; as also
of the Jesuit _Kircher_'s _Mundus Subterraneus_._

* * * * *

_An Account of a not ordinary _Burning Concave_, lately made at _Lyons_,
and compared with several others made formerly._

An opportunity being presented to revive the publishing of these Papers,
which for some Moneths hath been {96} discontinued by reason of the great
Mortality in _London_, where they were begun to be Printed; it hath been
thought fit to embrace the same, and to make use thereof for the gratifying
of the Curious, that have been pleased to think well of such
Communications: To re-enter whereupon, there offers it self, first of all a
Relation of an uncommon _Burning-glass_, not long since made in _France_,
in the City of _Lyons_, by one called Monsieur _de Vilette_, as it was sent
to the Publisher of these Tracts, in two Letters, whereof the one was in
_Latine_, the other in French, to this effect.

Concerning the Efficacy of Monsieur _de Villete_ his Burning Glass, all
what the _P. Bertet_ hath written of it, is true. We have seen the effects
of it repeated over and over again, in the Morning, at Noon, and in the
Afternoon, alwaies performing very powerfully; burning or melting any
Matter, very few excepted. The _Figure_ of it is round, being thirty
Inches, and somewhat better in _Diameter_. On one side it hath a Frame of a
Circle of Steel, to the end that it may keep its just Measure: 'Tis easie
to remove it from place to place, though it be above an hundred weight, and
'tis easily put in all sorts of postures. The _burning Point_ is distant
from the Centre of the Glass, about three Feet. The _Focus_ is about half a
_Louys d'or_ large. One may pass ones hand through it, if it be done
nimbly; for if it stay there the time of a second Minute, there is danger
of receiving much hurt.

_Green wood_ takes fire in it, in an instant, as do also many other Bodies.

A small peice of _Pot-Iron_ was melted, and _Seconds_
ready to drop down, in 40.
A _Silver Peice_ of 15 _Pence_ was pierced, in 24.
A _gross Nail_ (called _le Claude paisan_) was melted, i