Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/704

 V A R

V A R

ftfelf to the fluxion of the curve ; fo that the curvature heing Inverfely as the radius of curvature, and confequently, its fluxion as the fluxion of the radius itfelf directly, and the (quare of the radius inverfely, its variation would have been diccflly as the meafure of it, according to Sir Ifaac Newton's defi- nition, and inverfely as the fquarc of the radius of curvature. According to this notion, it would have been meafured by the angle of contact contained by the curve and circle of curvature, >h the fame manner as the curvature itfelf is meafured by the angle of contact contained by the curve and tangent. The reafon of this remark may appear from this example c . The variation of curvature, according to Sir Ifaac Newton's ex- plication, is uniform in the logarithmic fpiral, the fluxion of the radius of curvature in this figure being always in the fame ratio to the fluxion of the curve ; and yet, while the fpiral is produced, though its curvature decreafes, it never vanifhes, which muff, appear a ftrange paradox to thofe who do not at- tend to the import of Sir Ifaac's definition. — [ a Metb. of Flux, and inf. Series, p. 76. b Fluxions Art. 386. c Phil.

Tranf. N". 468. fefl. 6. p. 342 ]

The variation of curvature at any point of a conic fecYion, is always as the tangent of the angle contained by the diameter that pafies through the point of contact, and the perpendicu- lar to the curve at the fame point, or to the angle formed by the diameter of the fecfion, and of the circle of curvature. Hence the variation of curvature vanifhes at the extremities of either axis, and is greater! when the acute angle, contained by the diameter, paffing through the point of contafl and tin tangent, is leaft.

When the conic feflion is a parabola, the variation is as the tangent of the angle, contained by the right line drawn from the point of contact to the focus, and the perpendicular to the curve. VARICULA, a diminutive of the word varix, a term ap- plied by fome authors to the intumefcence of the veins of the tunica adnata in the eye, arifing from thick blood. VAR1E I IES, in natural hiftory, a word ufed to exprefs an ac- cidental change in fome body which is not eflential to it, and therefore does not confiitute a different fpecies. T' ie naturalifts of former ages have run into great errors, in imitating the accidental varieties of plants, animals, and mi- nerals for diflinfl fpecies. Many of them have called a plant a new fpecies, becaufe its flower, which fhould have been blue or red, is white on account of the poornefs of the foil, or Come other fueh reafon. Mr. Ray has eftablifhod a very good reft for varieties in botany ; he allows every thing to be a di- ftindl plant which will propagate itfelf in its own form by its feeds ; but fuch, as when (own, lofe their difference, and run back to the old ftandard, he accounts varieties, however great their diftinflions may appear. In the hiftory of fifhes as much confufion has been introduced by miffaking varieties for diftinfl fpecies as in botany. Artedi is the only author who has rationally attempted to bring this part of natural hiftory into order in this refpefl, and to fettle regularly the rules by which to diftinguifh real and eflential, from accidental differences. The principal grounds of the error of fuppofing varieties di- ftinfl fpecies of fifh, have been thel'e : The variable and in- fcohftant colour of fifhes has been miftaken for a fpecific dif- ference ; in this manner Rondeletius has defcribed many va- rieties of the turdi, labri, and other fifhes, under the names of diftinfl genera.

Others have paid the fame too great regard to the more con- stant varieties of colour, which are found only to differ in degree, in the feveral individuals of the fame fpecies, and their differences to be only in the degrees of the fame colour, which is much more intenfe in fome, and more re- mifs in others. Thefe differences can only make varieties of thefame fifh, the fpecies remaining always the fame. Of the fame kind are the mittakes of thofe who efteem fize or mag- nitude a fpecific character : and thus, out of the varieties of the fame fifh, occafioned by fcarcity or plenty of food, or other fuch occafions, make larger or fmaller fpecies. The place where fifh are caught, is alio another occafion of making new fpecies, with thefe fort of authors ; thus though the perca jiuviatilis of Uellonius, and the perca marina of other authors be the fame fifh, yet they are pretended to be different fpecies. The time of fpawning is alfo with fome made a diflinaion of fpecies ; and thus we find the common pike divided into three fpecies, according to its fpawning, in fpring, fummer, and autumn, which it does according to the heat or coldnefs of the climate. See the article Specific Names. All tbefe differences are falfe and frivolous, and the utmoft they can do, is to make what are properly called varieties though few of them are fufficient even for that. A falmon caught at fea, is not different from one of the fame brood caught in a river : and if the perca marina, falfly fo called, be a little different from the perca Jiuviatilis, yet if its fpawn will produce regular perca fluviatites, its difference can only amount to a variety, not a diftinfl fpecies. The trifling nature of diftinflion by colour, is fecn by the va- riety we daily fee in the colours of fome of our molt common fifh; as the tench, the eel, the falmon, and fome others, which vary more or lefs, from every change of the water ; all the other diftinflions, of fize and place, arc as frivolous j and

the giant and the dwarf,' the black and the white man, theAua- tic and the European, may as well be called diftinct fpecies of men, as thefe of fifties.

Finally, the time of fpawning is no efiential difference; for we daily fee the change of climate make changes of that kind in all creatures ; and even in the fame climate, and under the fame c i re um fiances, the fame fpecies of birds will afford fome individuals much earlier or later in laying their egg sthan others. Artedi Ichthyol.

VARIUS, in zoology, a name ufed by moft authors for a finall frefh-water fifh, common in brooks and running waters, and well known in England, by the name of the minow r or me- novo ; and called Phoxinus /avis by fome other Writers. It is diftingui (lied from other fifh of its fize, by being of av dufky brownilh olive culour on the back, by its having a yel- low line running on each fide, from the gills to the tail, be- low which the belly and fides are of a very varying colour ; in fome white, 'in others of a fine bright red, and in others, there is a line of a fine blue running on each fide ; and in others, the fides are variegated with yellow, brown, and red lines. Its fcales are fo extremely finall, that it has been generally fup- pofed to have none. Its mouth is very large. It is a very well tafted fifh, and if but a little larger, would be very much valued. Ray's Ichthyogr. p. 268.

Varius Mus, in the old authors ofzoography, a name ufett for the fame creature they otherwife called mus pontic us ; which feems to have been no other than our fquirrel. See the article Sciurus.

VARNISH (Cycl.) Amber Varnish. Amber Varnijh is pre- pared in the following manner : Put four ounces of amber in- to a crucible, and melt it with a fmall degree of heat, ant! pour it out upon an iron plate, when cold, reduce it to powder, and add to it two ounces of drying oil, that is, Iinfeed oil thickened by boiling it up with litharge, and one pint of oil of turpentine, and diflblve the whole together into a liquid Varnijh. Shaw's Lectures, p. 424.

This has been long a great fecrct in the hands of the traders in tbefe things ; but deferves to be made public, as a leading experiment towards the perfecting the arts of varnijhing and japanning.

China -V arnish. The China Varices have been always fa- mous; the manner of making which is fkid to be as fol- lows : Take crude VarniJJ) fixty ounces, common water the fame quantity, mix them well together till the water difap- pears ; afterwards put this "into a wooden veflel five or fix palms long, and two or three broad ; mix them together with a wood- en fpatula, for a whole day in the fummer's fun, for two days if in winter, and afterwards keep it in an earthen vefTel, covered with a bladder. The water will not unmix itfelf again: this is called the fun Varnijh. SccVarnih for Porcelain, infra. The oil of wood, called by the Portuguefe azcile de Pao, is made in the following manner : Take twenty ounces of that oil, which they call oil of wood, and ten drams of the oil of the fruit ; boil thefe a little together, and the oil will look yellow; then let it cool, and add to it five drams of quick lime powdered. To make the firfr. grounds called ca?nijeca 9 take Iwine's blood and quick lime powdered, of each an equal quantity; fpread this mixture upon the wood, and when it is dry, fmooth it with pumice-ftones.

To make the black Varnijh, take of the VarniJJ} prepared in the fun fixty ounces, fione black alum (fuppofed to be a fort of copperas J diftolvcd in a little water, three drams, and fe- venty drams of lamp-oil, called by the Portuguefe azcile de Canclea. Thefe things are all to be mixed together in a wood- en velTel, putting the lamp- oil in at twice, and ftirring the whole together with a wooden fpatula. The pitch-coloured Varnijh is made in the following manner : take oil of wood, crude, forty drams ; called da Pao, of the lamp-oil, called da Candea crude, forty drams; mix them together in the fun in a wooden velTel, in the-fame manner as the common VarniJJ) and water are ordered to be mixed in the firft procefs.

To make the red Varnijh, take ten drams of cinnabar, twen- ty drams of prepared Varnijh, and a little lamp-oil ; mix, them all together.

To' make the yellow Varnijh, take of the yellow colour ten drams, prepared Varnijh thirty drams, a little lamp-oil ; mix all together : and

To make a VarniJJ) of a mufk colour, take of the red Varnijh ten drams, and of the black Varnijh four drams ; mix them well together. Philof. Tranf, N°. 261. p. 524. Thefe are the accounts fent to the great duke of Tufcany by the jefuits in China : Dr. William Sherard communicated them to the royal fociety ; and to render the accounts ufeful to the world, he prefented with them the feveral fubftances mentioned ; thefe are depofited in the mufaeum of the fociety, and may ferve as inftruitio.is to all who are curious in this art.

Varnish for Porcelain. The Chinefe have of late years dis- covered a new kind of VarniJJ) for their ware : they call this Tjekinyeou, that is to fay, the brownifh gold varnifh; it is of the colour of the brown images, or of what we call coffee colour. The novelty of this has made it much efteemed : it is made in the manner of all their other varnifhes, by difiolv-