A _Thermometer_, thus marked and prepared, will be the fittest Instrument
to make a Standard of heat and cold that can be imagined. For being sealed
up, it is not at all subject to variation or wasting, nor is it liable to
be changed by the varying pressure of the Air, which all other kind of
_Thermometers_ that are open to the Air are liable to. But to proceed.
This property of Expansion with Heat, and Contraction with Cold, is not
peculiar to Liquors only, but to all kind of solid Bodies also, especially
Metals, which will more manifestly appear by this Experiment.
Take the Barrel of a Stopcock of Brass, and let the Key, which is well
fitted to it, be riveted into it, so that it may slip, and be easily turned
round, then heat this Cock in the fire, and you will find the Key so
swollen, that you will not be able to turn it round in the Barrel; but if
it be suffered to cool again, as soon as it is cold it will be as movable,
and as easie to be turned as before.
This Quality is also very observable in _Lead_, _Tin_, _Silver_,
_Antimony_, _Pitch_, _Rosin_, _Bees-wax_, _Butter_, and the like; all
which, if after they be melted you suffer gently to cool, you shall find
the parts of the upper Surface to subside and fall inwards, losing that
plumpness and smoothness it had whilst in fusion. The like I have also
observed in the cooling of _Glass of Antimony_, which does very neer
approach the nature of Glass,
But because these are all Examples taken from other materials then Glass,
and argue only, that possibly there may be the like property also in Glass,
not that really there is; we shall by three or four Experiments indeavour
to manifest that also.
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