So it at first appeared to Mr. Pictet; but upon a little consideration he found that it afforded only an additional proof of the reflection of heat: this I shall endeavour to explain to you. According to Mr. Prevost’s theory, we suppose that all bodies whatever radiate caloric; the thermometer used in these experiments therefore emits calorific rays in the same manner as any other substance. When its temperature is in equilibrium with that of the surrounding bodies, it receives as much caloric as it parts with, and no change of temperature is produced. But when we introduce a body of a lower temperature, such as a piece of ice, which parts with less caloric than it receives, the consequence is, that its temperature is raised, whilst that of the surrounding bodies is proportionally lowered. EMILY. If, for instance, I was to bring a large piece of ice into this room, the ice would in time be melted, by absorbing caloric from the general radiation which is going on throughout the room; and as it would contribute very little caloric in return for what is absorbed, the room would necessarily be cooled by it. MRS. B. Just so; and as in consequence of the mirrors, a more considerable exchange of rays takes place between the ice and the thermometer, than between these and any of the surrounding bodies, the temperature of the thermometer must be more lowered than that of any other adjacent object. CAROLINE. I confess I do not perfectly understand your explanation. MRS. B. This experiment is exactly similar to that made with the heated bullet: for, if we consider the thermometer as the hot body (which it certainly is in comparison to the ice), you may then easily understand that it is by the loss of the calorific rays which the thermometer sends to the ice, and not by any cold rays received from it, that the fall of the mercury is occasioned: for the ice, far from emitting rays of cold, sends forth rays of caloric, which diminish the loss sustained by the thermometer. Let us say, for instance, that the radiation of the thermometer towards the ice is equal to 20, and that of the ice towards the thermometer to 10: the exchange in favour of the ice is as 20 is to 10, or the thermometer absolutely loses 10, whilst the ice gains 10. CAROLINE. But if the ice actually sends rays of caloric to the thermometer, must not the latter fall still lower when the ice is removed? MRS. B. No; for the space that the ice occupied, admits rays from all the surrounding bodies to pass through it; and those being of the same temperature as the thermometer, will not affect it, because as much heat now returns to the thermometer as radiates from it. CAROLINE. I must confess that you have explained this in so satisfactory a manner, that I cannot help being convinced now that cold has no real claim to the rank of a positive being. MRS. B.