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VAR

Vapour-Bath, in medicine, is used when a sick person is madeto receive the vapours arising from some liquid matter placed overa fire. Vapour baths are very commonly used in Russia and®ther northern countries, not for any medical purpose, but as aluxury.

Vapours, in medicine, a disease properly called hyps, or the■hypochondriacal disease; and in men particularly, the spleen.

VAR1, in medicine, little, hard, and ruddy, tumours, which* r fcjnently infest the faces of young persons of a hot temperamentof body.

variable, in geometr y and analytics, is a term applied bymathematicians to such quantities as are considered in a variableor changeable state, either increasing or decreasing. Thus tin- ab-scisses and ordinates of an ellipsis, or other curve-line, are deno-minated variable quantifies; because these vary or change theirmagnitude together, the one at the same time with the other. See■Fluxions.

VARIATION OF THE COMPASS, is the deviation of themagnetic or mariner’s needle from the meridian or true north and® 0l >th line. It is now with more propriety called the declinationof the magnetic needle. See Magnetism. The variation of theNeedle was observed bv Mr. Bui rows, in the year 1530, to be 11°IV E. that is, if N. S. (tig. ft, Plate CLXXX.) represent the northai 'd south points of the horizon, and E. W. the east and westPoints, the needle then had the situation AB, so that the arch BN^ 11° 15'. After (hat, in (he year 1622, it was observed by Mr.Gunter to be buffi 0 east. In the year 1634, Mr. Gellibrand ob-served it to be 4° 5' E. In 1657, it was observed by Mr. Bond tohe nothing at all, that is, the needle placed itself in the situationh. N. and pointed directly to the north. After this, in the year1672, Hr. Halley observed it to be 2° 30' westward ; and again,in the year 1692, he found it 6° west. Since then, in the year1722, Mr. Graham, by most accurate experiments, found it to be14 13', and at present it is between 24° and 25° west of (he north.1 lie variation of the declination and inclination of the needle isvariable, and subject to no regular computation. What thequantity of both sorts of variation is in the several parts of theworld, is shewn in Dr Halley’s map of the world, improved fromthe observations of-Mr. Pound. l\ the sun’s true amplitude ora?imutb, found bv calculation, agree with the magnetic amplitudeor azimuth, found by observation, it is evident there is no varia-tion : but if they disagree, aud the true and observed amplitudesat the rising or setting of the sun, be both of the same name • thatis, either both north, or both south, their difference is the varia-tion ; whereas, if they be of different names, that is, one north andthe other south, their sum is the variation. Again, if the true andobserved azimuths be both of the same name, that is, both east orboth west, their difference is the variation ; but if they be of dif-ferent names, their sum is the variation : and to know whether thevariation be easterly or westerly, observe the following generalrule; let the observer’s face be turned towards the sun, then if thetrue amplitude or azimuth be to the right hand, the variation iseasterly ; but if to the left, westerly. To illustrate this, letN. E. S. W. (fig. 10,) represent a compass; and suppose the simis really E.b.S. at the time of observation, but the observer seeshim off the east point of the compass, and so the true amplitude orazimuth of the sun is to the right of the magnetic, or observed :here it is evident, that the E.b.S. point of the compass ought to lie"'here the east point is, and so the north where the N.b.W. is;consequently the north point of the compass is a point too far ea't,•bat is, the variation in this case is easterly. The same will hold•Wen the amplitude or azimuth is taken on the west side of themeridian. Again, let the true amplitude or azimuth be to the leftband of the observed ; thus suppose thesun is really E.b.N. at thebine of observation, but the observer sees him off the east point of4 be compass, and so the true amplitude or azimuth to the left of•be observed : here it is evident, that the E.b.N. point of the com-pass ought (o stand where the east point is, and so the nortf) where•he N.b.E. point is; consequently the nortli point of the compassesbes a point too far westerly, so in this case the variation is west.J he same will hold when the sun is observed on the west side ofJfie meridian. Suppose the still’s true amplitude at rising is found12’ M E ‘ 14 ° 2<y N - but b .V the compass it is found to be E, 26°ark r 1 ' ' Required the variation, and which way it is. Since theyboth the same way, therefore,

From the magnetic amplitude...E. 26° 12' N.

take the true amplitude.E. j 4 ° 20 ' N.

and there remains the variation....,.li* 52 ' E.

which is easterly, because in this case the true amplitude is to theright of the observed.

Variation of Curvature, iti geometry , is used for that ine-quality or change which takes place in the curvature of ali curvesexcept the circle, by which their curvature is more or less in dif-ferent parts of them ; and this variation constitutes the quality ofthe curvature of any line.

VARIETY, or VARIETAS, in botany, is a change in someless essential part or quality ; as colour, size, pubescence, or age.Externally ; by the platting or interweaving of the branches ; bybundling or uniting of several stalks into one broad flat one; bythe greater breadth, or narrowness, or curling of leaves; by be-coming awnless, or smooth, or hirsute. Internally, by becomingmutilated in the corolla, or having one larger than ordinary ; byluxuriancy, multiplication, or fulness ; by becoming proliferous,or crested ; by bearing bulbs instead of seeds; or being viviparous.The usual causes of variation are, climate, soil, exposure, heat,cold, winds, and culture; and often disease; hence mordus, inbotany, is synonymous with varietas.

VARIOLAS, the small-pox . See Medicine.

Variola Vaccinje, or Cow-pox, the name commonly givento a very singular disease, which has occupied a great snare 0 , tneattention of medical men. See Vaccina rioN.

VARIX, in medicine, the dilation of a yem, arising from toogreat abundance or thickness of the blood.

VARNISH, a clear liquid composition, which, by age and ex-posure to the air, becomes hard, without losing its transparency :it is enypioyed by painters, carvers, gilders, and other artisans, forimparting lustre to their works, while it defends or preserves themfrom the effects of dust, moisture, and air. Varnishes are of va-rious colours, derived from the ingredients of which they consist:their bases are resins, dissolved in fixed oil, in volatile oil, or inalcohol ; and, accordingly as either of .these fluids are used, thevarnishes are distinguished by the names of fat or oily, essential,and spirit-varnish. Before a resin is dissolved in a fixed oil, it isnecessary to render the oil drying. For this purpose the oil isboiled with metallic oxides; in which operation the mucilage ofthe oil combines with the metal, while the oil itself unites with theoxygen of the oxide. To accelerate the drying of this varnish, itis necessary to add oil of turpentine. The essential varnishes con-sist of a solution of resin in oil of turpentine. The varnish beingapplied, the essential flies off and leaves the resin. This is usedonly for paintings. When resins are dissolved in alcohol, the var-nish dries very speedily, and is subject to crack ; but this fault iscorrected by adding a small quantity of turpentine to the mixture,which renders it brighter, and less brittle when dry. The follow-ing are the ingredients in the different varnishes. For Toilet-boxes, Cases , Fans, Sec. Dissolve two ounces of gum-mastich,and eight ounces of gum-saudarach, in a quart of alcohol; thenadd four ounces of Venice turpentine. For Wainscots, Cane-chairs, Iron chairs, Grates. Dissolve in a quart of alcohol eightounces of gnm-sandarach, two ounces of sced-iac, four ounces ofresin; then add six ounces of Venice turpentine. For Fiddles,&c.. Put four ounces of gum-sajidarach, two ounces of lac, twoounces of gum-maffich, one ounce of gum-eiemi,, into a quart ofalcohol, and hang them over a slow hre till they are dissolved;then add two ounces of turpentine. To employ Vermilion forpainting Equipages. Dissolve in a quart of alcohol six oqttces ofsandarach, three ounces of gum-lac, and four ounces of resin ; af-terwards add six ounces of turpentine. Gold-coloured Farr.sh,Pound separately four ounces of stick-lac, four ounces of gam-boge, four ounces of dragon’s blood, four ounces of annotta, andone of saffron: put each of them sepuutely into a quart of alcohol,and expose them for five days in a narrow-mouthed bottle to thesun, or in a very warm room, shaking them fieqiu otly, When allare melted, mix them together. In order to make silver imitategold exactly when covered with this varnish, the quantity of ingre-dients must be somewhat greater. The method o f giLbng-sdver-icaf, Sec. with this varnish is as follows: The silver-leaf being fixedon the subject, in the same-manner as gold-leaf, by the interposi-tion