ascertaining high degrees of heat: for this purpose he employs small cubes of dry clay; because that species of earth has the remarkable property of contracting in its bulk, when submitted to the fire, and not again expanding, on suddenly exposing it to the cold air. In order to ascertain the precise degree of heat in an oven, he puts one of his clay-cubes into it; and, after having acquired the temperature of the place, he immediately plunges it into cold water. Now, the size of the cube (that was exactly adjusted to half an inch square) is measured between two brass rules, the sides of which are somewhat obliquely disposed, so as to form an irregular groove, into which the cube may be slidden. In proportion as the bulk of the latter has been contracted by heat, it passes down deeper between the scales, on which the various degrees of temperature have been previously marked. Thus, when the division of the scale commences from the point of red heat visible in day-light, and the whole range be divided into 240 equal parts, it will be found that Swedish copper melts at 28; gold at 32; iron at from 130 to 150 degrees: above this point, the cubes could not be heated. But, if one of these clay squares be put into an oven where other materials, such as bread, earthen-ware, &c. are to be baked, they may be usefully employed, for regulating the necessary degree of heat.
THIGH, a term applied to that part of the human body, which is situated between the pelvis, or bason, and the knee; thus forming the upper portion of the lower extremity. The principal affections to which this limb is liable, being Fracture, Dislocation, and sciatica, it will be unnecessary to enter into any farther discussion on these heads; as they have been already treated of, vol. ii. p. 331; vol. iii. pp. 136, and 488.
THIRST, is an uneasy sensation, which arises from a deficiency of saliva, for moistening the mouth, and lubricating the throat.
Thirst is generally occasioned by the use of strong, salted, or highly-seasoned food: a moderate degree contributes to the preservation of health; as it requires a certain proportion of drink, to promote digestion; but, if it become excessive, it is in most cases a symptom of fevers, dropsies, &c.
The most effectual way of alleviating thirst, will be the use of diluted vegetable acids; or the chewing of a crust of bread with a little water, which liquid may be gradually swallowed. Where this unpleasant sensation, however, is consequent on any disease, the removal of the latter, together with the aid of diluent liquors adapted to its nature, and taken in small quantities, will also prevent the return of thirst. In other cases, where the use of acids or profuse draughts of diluents, might be productive of injury to the constitution, this complaint may sometimes be obviated, by chewing the root of the pellitory, or some similar substance, which excites and increases the flow of saliva. Lastly, as thirst is often the concomitant of excessive Hunger, and may sometimes occur at sea, the adoption of the expedients pointed out in that article, will generally afford relief.
THISTLE, or Carduus, L. a genus of plants, comprising 38 species; 10 of which are indigenous: the following are the principal:
