second set. It may proceed either from some of the first set having been suffered to remain in the jaw, after the second has appeared; from a want of space in the jaw-bone, or, from mal-conformation. In these cases, the only effectual remedy is that of extracting such of the teeth, as by their situation obstruct their neighbours, and sometimes occasion considerable distress.
If the teeth should be loosened by external violence, they may again be fixed, by pressing them firmly into the sockets, and preserving them in that situation, either by a silk, or other ligature attached to the adjoining tooth: the patient, however, ought to subsist entirely on spoon-meat, or other soft and liquid food, till the desired effect be attained. But, where this separation arises from a sponginess or weakness in the gums, mild astringents, for instance, a solution of alum and sugar, tincture of bark, catechu, &c. will serve to consolidate the surrounding parts.
For cleansing and preserving the teeth, burnt bread, or bark, applied by the small finger, or on a piece of calico, will be found a safe and useful dentifrice.—Lord Dundonald recommends, for this purpose, a weak solution of Soda.
Lastly, in cases where a substitution of artificial teeth should be deemed necessary, these useful bones ought to be manufactured from the tooth of the Hippopotamus, or river-horse; and on no account whatever to be taken from other persons. There are instances on medical record, where the latter practice has communicated infectious diseases, and eventually proved falal.
TELESCOPE, one of the most useful optical instruments, consisting of a long tube furnished with several glasses, for the purpose of viewng distant objects.—This term is mostly applied to the larger kinds of telescopes; the smaller ones being called perspective-glasses, spy-glasses, opera-glasses; and a particular species, which is much brighter than any other, is known under the name of night-glasses.
Telescopes are of extensive utility, both in naval and military pursuits, but especially for contemplating the celestial bodies: hence the merit and honour of their original invention have been claimed by many ingenious men. According to the most accurate accounts, however, the authentic contriver was Zacharias Jansen, a Dutchman, who produced his first instrument in the year 1590. Since that period, various improvements and additions have been made by Galileo, Kepler, Huygens, Mersennus, Gregory, Short, Ramsden, Dollond, Adams, and numerous other philosophers and artists. The most important are, those accomplished by Dr. Herschel, whose grand instrument, when furnished with proper glasses, magnifies upwards of six thousand times.
It would be incompatible with our plan, to enter into the rationale, or an account of the principles on which telescopes are in general constructed. We shall, therefore, only remark, that a complete description of the machinery of Dr. H.'s noble instrument is inserted in the Philosophical Transactions of the Royal Society, Part ii. for 1795;—and we shall proceed to state the principal patents
