Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/528

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branch of fir ftript of its leaves, or that fort of fucus called the/«i ragged Jiaf. Another very common kind in fome parts of the world, cfpecially in Syria, but lefs frequent with us, is the body called by authors lapis judakus : thefe are fuppofed, in fome fort, to referable an olive, fwelling from a (hurt {talk to a large thick and fliort body of an oval figure, and marked very elegantly with longitudinal fur- rows, and in the different fpecies with very differently fhaped tubercles. Of this fhape there are alfo fome perfectly fmooth.

We have alfo with us great numbers of a kind approaching to thefe, but having longer ftalks and fmaller bodies, and thefe we meet with of all fizes, from three inches in length down to the bignefs of a barley-corn ; and there are at times found fome of all the intermediate figures, between thefe tumid ones and the long and flendcr fort. We have numbers alfo of various lengths, and varioufly fur- rounded with granuke of afhape nearly cylindric, and befide the bodies thcmfelves, we meet with impreihons of all the kinds on our flints in gravel-pits. The j pines themfelves are ufu- ally bedded in the irrata of chalk, though fometimes they are found in the ftone-quarries, and fometimes, but that molt rarely, bedded in clay, or loofe among gravel. Hill's Hilt, of Foil", p. 652. SPINNING (Cyc/.)- — The art of /pinning, which nature has given to many animals of different kinds for their prcfervati- on and other purpofes, is not confined to the inhabitants of the eartli or air alone, but is even extended to thofe of the fea. Mr. Reaumur has {hewn, by a feries of curious expe riments, that the common mufcle, and fome other lhell-nfh of the fea, poffefs it in a great degree of perfection. See the article Muscle.

But he obferves, that though the workmanfhip is the fame, the manner of producing it is very different. Spiders, ca- terpillars, and the like, make threads of any length that they pleafe, by making the vifcous liquor, of which they are formed, pafs through a fine perforation in the organ ap- pointed for this /pinning : but the way in which the mufcles form their threads is very different, as the former refem- bles the work of the wire-drawer, fo this does that of the founder, who cafh metals in a mould. The canal of the or^an, deiKned for the mufcle's /pinning, which from its fhape is commonly called its tongue, is the mould in which its thread is caff, and gives it its determinate length. Mem. Acad. Par. 1711. SPINOSA, in zoology, the name by which the Italians call

the porcupine. See the article Histrix. SPINOSE-Att/", among botaniifs. Seethe article Leaf, SPINOSI pi/ces, in zoology, fiich fifties as have fome of the rays of their backftns running out into thorns or prickles, as the pearch, E3Y. Willughby, Hift. Pifc. p. 271. SPINOZISM (CycL) — We have an examination of Spwozi/m, and of Mr. Bayle's objections againir. this fyftem, by Monf. de Jariges, in the Mem. de 1'Acad. de Berlin, Tom. I. p. i2J. and Tom. II. p. 295. Wolfius has alfo given a refutation of Spinoza, in his Theol. Nat. Part 2. SPINTHER, among the Romans, a kind of bracelet which the women, in the fir ft ages of Rome, ufed to wear on tfo upper part of their left arm. SPINUS, in the natural hiftory of the antients, the name of a foflile body of a very remarkable quality; for accordin to the accounts of Theophraflus, and other authors of the greateft credit, if. broke to pieces, and thrown in an heap expofed to the fun, it took fire and burnt, and that the more, if moiftened or fprinkled with water.

It feems to have been a fublrance nearly allied to what they called the lapis ihracius, but with this remarkable quality, both of them feem to have been of the clafs of the harder bitumens, and are wholly unknown to us. Some late writers have imagined, that the common black flate-ftone, to frequent with us in the coal-pits, was the fubitance called by Theophraflus, and the antients, by this name, but it has none of the qualities attributed to the /pinus. HilPs Theophraflus, p. 35. Spinus, in zoology, the name of a fmall bird, called by fome ligurinut, and in Englifh the //kin. Its head is black, and its neck and back green. The neck, however, has fome flight admixture of a blackifh tinge, and the roots of the backfeathers have alfo fome bhickifhnefs. Its rump is of a greenifh yellow, as aie alfo its breaft and throat. Its belly is white, and its tail is yellow underneath, with fome brown- !fh fpots. The female is paler coloured than the male, and its throat, and its fides, under the wings, are whitifh with {freaks of brown. It is common in Germany and England, and is kept in cages for its finging. In winter thefe birds fly in large flocks. Ray's Ornitholog. p. 102. SPl'POLA, in zoology, the name of a fmall bird of the lark kind, of which there are, according to Aldrovand, three fpecies, fufpectedby Mr. Ray to be only varieties of the fpipoletta, or tordlno of the Venetians. Aldrovand. de Avib. lib. 17. cap. 26. See the next article. SPIPOLETTA, in zoology, the name of a fmall bird of the lark kind, called tor dim .by the Venetians, and feeming to bethe Jopparola, as alfo the gri/olajwd/pipolaoi' Aldtavuidus. 3

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It is fmaller than the common lark; its head, neck, moul- ders, and back, are of a greyifh colour, with an admixture of green ; its breaft and belly white, and its throat fpotted. The female differs from the male, in that her belly is yellow. The wing-feathers are of a dufky brown, with whitifh or yellowifh edges. Its tail is moderately long and part of the feathers are fnow-white, the reft brown or blackifh. The length of the heel diftinguifhes this bird from all others, except the lark kind, and it differs from all the fpecies of larks in the colour of its beak and le^s, which are black. It is common in the markets of Venice and other places. Ray's Ornitholog. p. 153. SPIR/EA, in botany, the name of a genus of plants, the characters of which are thefe. The flower is of the rofa- ceous kind, being compofed of feveral petals arranged in a circular form. The piftil arifes from the cup, and finally becomes a fruit compofed of feveral fmall pods, containing oblong feeds.

The fpecies of fpiraa, enumerated by Mr. Tournefort, ars thefe. I. The willow-leaved fpirza. 2. The opulus-leaved fpirxa. 3. The fpirtsa with hypericum leaves, not in- dented. And 4. the Spanifh fpirxa with crenated leaves, rcfembling thofe of the hypericum. town. Inft. p. 618. The feveral fpecies of this plant are very common in our gardens, and make a very beautiful figure. They are pro- pagated either by fuckers, which they produce in great abundance, or by laying down the tender branches of the old plants. When they have taken root, they fliould be removed into the nurfery for two or three years, and will then be fit for tr;,nfplanting in the places where they are to remain. Miller's Gard. Diet. SPIRAL {CycL)— As a curve may approach continually to a right line, or to another curve, while they are both pro- duced, and yet never meet it, fo a fpiral line may approach continually to a certain point, and not reach it in any number of revolutions, how great foever, that can be aflign- cd. This happens in the logarithmic, or logifticyJ>/ra/, and in feveral others. See Mac Lamm's, Fluxions, Book 1. p. 283,. feq.

Some of thefe fpirals, after having made an infinite num- ber of revolutions, is faid, in the' modern ftile, to reach that certain point, and yet the length of the fpiral may be finite, or equal to an aflignable line. Propofitions, expreffed in this manner, feem the moft myfterious of paradoxes; but the wonder difappears, when we know it amounts to no more than that a line may continually increafe, and yet the increments acquired may decreafe in fuch a manner, that it fhall never amount to a given line. Spiral of Archimedes. TheyJ>/r«/area CABDE, is equal to

one third part of the circle, defcribed with the radius CE. In like manner, the whole fpiral area, ge- nerated by the ray T.- drawn from the point C to the curve, when it makes two revoluti- ons, is the third part of a fpace double of the circle defcribed with the radius 2 C E ; and the whole area, generated by the ray from the beginning of the motion, till after any number of revolutions, is equal to the third part of a fpace that is the fame multiple of the circle defcribed with the greateft ray, as the number of revolutions is of unit. Any portion of the area of the fpiral, terminated by the curve CfflA, and the right line C A, is equal to one third of the fecfor C A G, terminated by the right line C A, and C G, the fituation of the revolving ray, when the point that defcribes the curve fets out from C. See Mac Laurin's Fluxions, Introd. p. 30, 31. Spiral of Pappus, a fpiral formed on the furface of a fphere, by a motion analogous to that by which the fpiral of Archimedes is defcribed in piano. See the article Spiral, Cycl.

This fpiral is fo called from its inventor Pappus. Collet}. Mathem. lib. 4. prop. 30.

Thus, if C be the center of the fphere, A R B A a great

circle, "