FREE CALORIC.

meter) we may estimate, in the most exact man-ner, the various dilatations of any solid body byheat. The body we are now <;oimi to submit totrial is this small iron bar; 1 fix it to this appara-tus, (Plate I. Fig. 1.) and then heat it by light-ing the three lamps beneath it: when the barexpands, it increases in length as well as thick-ness; and, as one end communicates with thiswheel-work, whilst the other end is fixed and im-movable, no sooner does it begin to dilate thanit presses against the wheel-work, and sets in mo-tion trie index', which points out the degrees ofdilatation on the dial-plate.

EMILY.

This is indeed a very curious instrument ; butI do not understand the use of the wheels: wouldit not be more simple, and answer the purposeequally well, if the bar pressed against the index,and put it in motion without the intervention ofthe wheels?

MRS. B.

The use of the w heels is merely to multiply themotion, and therefore render the effect of thecaloric more obvious : for it the index moved nomore than the bar increased in length, its motionwould scarcely be perceptible; but by means ofthe wheels it moves in a much greater proportion,