G L A
the plane inclines towards the fire. Vid. Phil. Tranf. ibid.
p. 343» 344-
Neither the draught of air up the chimney, nor attracti- on or repulfion are the caufe of thefe phenomena. It feems rather owing to the f welling of the tube towards the fire ; for allowing fuch fwelling, gravity muft pull the tube down, when fupported near its extremities horizontally ; and a frefh part being expofed to the fire, and fwelling out again, muft fall down again, and fo on fucceflively j which will produce a rotatory motion towards the fire. If the tube be fupported by two other tubes, and thefe be brought near to each other and to the center of the fupport- ed tube, then its parts hanging over on each fide, being larger than the part which lies between the fupporters, will by their weight, pull downwards, and confequently force the middle part, refting upon its two props, upwards ; and being lefs advanced towards the fire, as being lefs heated, will, by their oblique Situation, pull the middle part back- wards alfo from the fire, which will caufe a rotatory re- grefiive motion quite contrary to what the tube had when fupported near its extremities. And when a fingle tube lies inclining oppofite to the fire, either to the right hand or to the left, out of a plane perpendicular to the fmface of the fire, gravity will not permit the curved part to reft, but pull it down till it coincides with a plane perpendicular to the horizon ; and confequently, as new curves are gene- rated, new motions will be fo too ; that is, the tube will be made to move about its axis, with this difference, when the tube inclines to the right hand, the motion will be from eaft. to weft ; when to the left hand, from weft to eaft. The juftnefs of this reafoning is made nianifeft, by bending a wire and fupporting it firft near its extremities, then near its center on each fide, afterwards inclining it to the right and to the left; the bending in every cafe reprcfentingthe curved part of the tube next the fire. This folution of the phe- nomena is rendered the more probable from hence, that when four fupporters were made ufe of, one at each extre- mity, and two near the middle, there was no motion at all either backward or forward. Nor does the increafe of contact hinder the motion, becaufe the plate of glsfs was fo broad as to have a much greater contact with the tube, and yet both the rotatory and regreflive motions were mani- feft. Philof. Tranf. ibid. p. 347, 348. The experiments fucceeded beft with tubes about twenty or twenty two inches long ; the diameter about ■& inch ; and they had in each end a pretty ftong pin fixed in cork, for an axis to roll with on the fupporting tubes.
Glass, how to cement the cracks of glafs receivers. See Receiver.
Glass. To take the impreflion of antique gems in glafs. See Gem.
GLAss-wort. See Kali.
GLAUCEDO, a term ufed by fome medical writers, for the difcafe more ufually called glaucoma. See the articles Glaucoma and Cataract, Cycl.
GLAUCIDIUM, in zoolygy, the name ufed by fome authors, for the fmall ei' fpecics of glaucus, the fecond fpecies of Rondel et ius. Rays Ichthyolog. p. 296. See the article Glaucus.
GLAUCIUM, in zoology, the name given by Bellonius to a fpecies of duck, feeming by his defcription to be the fame with the capo roffb, or anas j "era fufca minor, the fmall brown wild duck of authors. See Capo Rojfo.
Glaucium, horned Poppy, in botany the name of a genus of plants, the characters of which are thefe. The flower is of the rofaceous kind, being ufually compofed of four leaves difpofed in a circular order. The cup confifts of two leaves, and from it there arifes a piftil, which finally becomes a long flender unicapfular pod, or feed veflel, of a cylindric form, containing a number of roundifh feeds. The fpecies of glaucium enumerated by Mr. Tournefort arc thefe. 1. The fmooth yellow flowered glaucium. 2. The hairy fcarlet flowered glaucium. 3. The fmooth fcarlet flower- ed glaucium. 4. The glaucium with violet coloured flowers. Tourn. Inft. p. 254.
GLAUCUS, in zoology, the name of a genus of fifties, of which Rondeletius has defcribed three fpecies. The firft, or more common kind, is a broad fifli approaching to the figure of the turbut, but very thin ; its colour on the back and fides is a dufky olive, and on the belly white, and tt has on each fide three or four black fpots. Its fcales arc very fmall and rounded, its mouth is moderately large, but its teeth are extremely fmall ; the whole infide of its mouth is tinged with blue. Its gill fins are fmall, and its back fins two in number, but the anterior fcarce deferving the name of a fin, being only a feries of loofc prickly rays or nerves ; thefe are feven in number, and the foremoft of them bends forward pointing toward the head, the other all ftoop to- ward the tail. The tail is extremely large, and more fork- ed than almoft in any other fifh ; the tips of the forks are tinged black. This is caught in the Mediterranean. Wilhigh. Hift. Pifc. p. 298. The fecond kind has much of the figure of the firft, and
G L A
is called by fome giaucidium, as being a diminutive of glau* cm ; it never arriving at the fize of the former. This has alfo an undulated line running on each fide from the membrane of the gills, to the middle of the body, from whence it is continued ftrait to the tail ; whereas in the common glaucus, this line runs ftrait all the way. The fins alfo of this arefpotted with blacky and its body is fome- what lefs broad in proportion to its length. Rondelet. dePifc, p. 460.
The third kind differs from the former in its havino- very ftrong and fharp teeth, and having its fide lines from the gills much more finuous, and waved, refembling the curl- ing of a ferpent in motion. The back, to this line, is of a deep bluifh black, below this line it is perfeflly white, Rondelet. de Pifc. p. 400.
GLAUX, ?nilk wort, in botany, the name of a genus of plants. the characters of which are thefe. The flower confifts of one leaf, formed into the fhape of a bell, fometimes open at the end, and fometimes fhut, and divided into fevcral feg- ments. From the middle of the flower there rifes a piftil which afterwards ripens into a fruit or {hell, which is ufin ally of a globular figure, and opening at the extremity, fhews a great number of fmall feeds fixed to a placenta. The fpecies of glaux enumerated by Mr. Tournefort are thefe.
1. The common fea kind. 2. The white flowered fea kind, and 3. the marfh glaux with leaves like thofe of purfelain and a ftriated fhut flower. Tourn. Inft. p, 88.
GLAZING. The Roman method of glazing fome of their urns, might give our workmen a hint toward a method greatly fupericr to any thing now in pra&ice for the glazing earthen ware. There are a fort of red urns found in York- shire, which are, inftead of glazing, covered all over in- fide and out with a fine coral coloured varnifh, which gives them a beauty, no earthen ware of our times can come up to ; and is not only far more durable than our way of do- ing it with lead, which is apt to crack and fly, both with wet and with heat, but far more fafe and wholfome. Lead being well known to be a vapourable metal, and its fumes very noxious, there is great reafon to fufpect that it muft be un- wholefome when brought to the fire. This antient glazing feems to have been done either by the brufh, or elfe by dip- ping,^ for both infide and out are varnifhed with equal re- gularity ; and fomething may be gueffed at as to the mate- rials they ufed in it from what Pliny has left us. This au- thor occafionally obferves, that fuch earthen ware as Was painted with bitumen, never loft its beauty ; and afterwards that it was a cuftom to cover over whole ftatues with this fort of glazing, which he obferves did net only make a fmooth coat, but funk into the matter of the ftone or earth, and therefore this could not be likely to crack and fly off like our lead coat on plates, &c.- which is merely a cruft laid over them. Hook's Philof. ColleCt. p. 89.
Black Glazing is made of lead afhes eighteen meafuresj iron filings three, copper afhes three, and zaffer two mea- fures. This when melted will make a brown black ; and if you want it blacker, add more zaffer to it.
Blue Glazing is thus prepared : take lead afhes one pound, clear fand or pebble two pound, fait two pound, white cal- cined tartar one pound, venice or other glafs fixteen pounds, zaffer half a pound ; mix them well together, and melt them for feveral times, quenching them always in cold water. If you would have it fine and good, it will be proper to put the mixture into a 'glafs furnace for a day or two.
Brown Glazing is made of common glafs and man^anefe or brown ftone, of each one part, and lead glafs twelve parts.
Flefo-colour Glazing is made of twelve parts of lead afhes, and one of white glafs.
Gold coloured Glazing. To make gold coloured glazing, take of litharge parts iij. of fand or calcined flint, p. i. pound, and mix thefe very well together, then rim them into a yellow glafs with a ftrong fire. Pound this glafs and grind it into a fubtile powder, which moiften with a well faturated folution of filver, make it into a pafte ; which put into a crucible, and cover it with a cover; Give at firft a gentle degree of fire, then increafe it, and conti- nue it till you have a glafs, which will be green. Pound this glafs again, and grind it to a fine powder ; moiften this powder with fome beer, fo that by means of an hair pencil you may apply it upon the veffels, or any piece of earthen ware. The veffels that are painted or covered over with this glazing, muft be firft well heated, then put under a muffle, and as foon as the glafs rims, you muft fmoak them, and take out the veflels. Mr. Heinfius of Peterfburg^ who fent this receipt to the Royal Society, ufes the words afflare debes fumum, which is rendered fmoak them, in the Tranfactions. Phil. Tranf. N°. 465. 3 6:
Green Glazing may be prepared of eight parts of litharge,' eight parts of venice glafs, four parts of brafs duft ; or, of ten parts of litharge, twelve of flint or pebble, and one of as ajlum, or copper alh.es.
Jrsn*
