ers?

MRS. B.

A thermometer is constructed exactly on the same principle, and these
tubes require only a scale to answer the purpose of thermometers: but
they would be rather awkward in their dimensions. The tubes and bulbs of
thermometers, though of various sizes, are in general much smaller than
these; the tube too is hermetically closed, and the air excluded from
it. The fluid most generally used in thermometers is mercury, commonly
called quicksilver, the dilatations and contractions of which correspond
more exactly to the additions, and subtractions, of caloric, than those
of any other fluid.

CAROLINE.

Yet I have often seen coloured spirit of wine used in thermometers.

MRS. B.

The expansions and contractions of that liquid are not quite so uniform
as those of mercury; but in cases in which it is not requisite to
ascertain the temperature with great precision, spirit of wine will
answer the purpose equally well, and indeed in some respects better, as
the expansion of the latter is greater, and therefore more conspicuous.
This fluid is used likewise in situations and experiments in which
mercury would be frozen; for mercury becomes a solid body, like a piece
of lead or any other metal, at a certain degree of cold: but no degree
of cold has ever been known to freeze spirit of wine.

A thermometer, therefore, consists of a tube with a bulb, such as you
see here, containing a fluid whose degrees of dilatation and contraction
are indicated by a scale to which the tube is fixed. The degree which
indicates the boiling point, simply means that, when the fluid is
sufficiently dilated to rise to this point, the heat is such that water
exposed to the same temperature will boil. When, on the other hand, the
fluid is so much condensed as to sink to the freezing point, we know
that water will freeze at that temperature. The extreme points of the
scales are not the same in all thermometers, nor are the degrees always
divided in the same manner. In different countries philosophers have
chosen to adopt different scales and divisions. The two thermometers
most used are those of Fahrenheit, and of Reaumur; the first is
generally preferred by the English, the latter by the French.

EMILY.

The variety of scale must be very inconvenient, and I should think
liable to occasion confusion, when French and English experiments are
compared.

MRS. B.

The inconvenience is but very trifling, because the different gradations