44

FItEE CALORIC.

MRS. B.

The thermometer fell considerably.

CAROLINE.

And does not that prove that cold is not merelya negative quality, implying simply an inferior de-gree of heatf The cold must be positive, since itis capable of reflexion.

• MRS. B.

So it at first appeared ; but upon a little consi-deration it was found that it afforded only an ad-ditional proof of the reflexion of heat: this Ishall endeavour to explain to you.

According to Mr. Prevost’s theory, we supposethat all bodies whatever radiate caloric; the ther-mometer used in these experiments thereforeemits calorific rays in the same manner as anyother substance. When its temperature is inequilibrium with that of the surrounding bodies,it receives as much caloric as it parts with, and nochange of temperature is produced. But whenwe introduce a body of a lower temperature, suchas a piece of ice, which parts with less caloricthan it receives, the consequence is, that its tem-perature is raised, whilst that of the surroundingbodies is proportionally’ lowered; and as, fromthe effect of the mirrors, a more considerable ex-1 change of rays takes place between the ice and