"... of may allow us to say that "this object is hotter or colder than that one." But even this apparently simple statement is fraught with pitfalls for the unwary. For example, take hold in turn of a block of , a piece of expanded and a rod of , all near room temperature but differing slightly slightly in temperature from one another. It is not easy to make any useful statements about which is hotter or colder. This means, of course, that the is a poor thermometer, but the reasons for this being so are by no means straight-forward: they are related to the way in which sensations of hotness and coldness are generated in the human body ..."