Note 2 — INTRODUCTION.

That the terms hot and cold are relative, as to our feelings, fact and observations abundantly prove. Dr. Fordyce (Phil. Trans. vol. 64 & 65) heated a room by stoves to two hundred and sixty degrees of Fahrenheit's scale, and remained in it for some time without great inconvenience. But different metallic substances, as the lock of the door, his watch and keys lying on the table, could not be touched without burning him: and although an egg became hard, and his pulse beat one hundred and thirty-nine per minute, yet a thermometer placed in his mouth was only two or three degrees hotter than common. He perspired profusely. Jenning's steam bath will heat the air in contact with the naked body from one hundred to one hundred and twenty degrees, a heat sufficient, as it is in the aqueous vapour, resulting from the combustion of alcohol or strong spirit, to induce a copious diaphoresis in less than half an hour. Having tried this experiment in several cases, I can only say, that I effected in the course of an hour, what, under ordinary circumstances, would require twelve or twenty-four, viz. a copious perspiration, and that too without the exhibition of sudorifics. The practice is an old one not only among civilized nations, but aborigines. It is nevertheless worthy of adoption.

Frozen mercury cannot be touched without experiencing a sensation similar to that of an ignited body, although directly opposite to heat.