True; we shall now plunge the bulbs into hot water, ([Plate I.] Fig. 2.) and you will see both liquids rise in the tubes; but the spirit of wine will ascend highest.
CAROLINE.
How rapidly it expands! Now it has nearly reached the top of the tube, though the water has hardly begun to rise.
EMILY.
The water now begins to dilate. Are not these glass tubes, with liquids rising within them, very like thermometers?
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.