Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/934

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VACCA marina, in zoology, a name fometimes ufed for the manatiy or fea cow. See the article Ma- NATI, Suppl.

VALERIAN (Suppl)— Greek Valerian, a name frequently ufed for the pokmonium of botanifts. See the ar- ticle PoLEMONlUM, Suppl.

VALERIANOIDES, in botany, a name given by Petiver to the cephalantbus of Linnasus. See the article Cephalan- thus, Append. VALLEY (Cycl.) — Valleys, in building, denote the gut- ters over the flecpers in the roof of a building. Build. Diet, in voc.

VALLOR, Vallow, or Vate, among country people, a hollow. mould, in which anew-made cheefe is prefTed. Ruff. Diet, in voc.

VARVELS, in falconry, fmall filver rings about a hawk's leg, with the owner's name on them. Ruft. Diet, in voc.

VATE, in the making of cheefe. Sec Vallor, fupra.

VAULT [Suppl.) — Going to the Vault, a term ufed by fportf- men for a hare's taking the ground like a coney, which fhe fometimes does. Ruff. Diet, in voc.

VEGETABLE (Suppl.)— Perfpiration ^/Vegetables. See Perspiration, Append.

VELLICULA, a name fometimes ufed for the forjieula, an infect called in Englifh the car-wig. See the article Ear- wig, Append.

VELLING, a term ufed by hufbandmen in the weft of Eng- land for plowing up by the turf. Ruff. Diet, in voc.

VENTILATOR, a machine by which the noxious air of any clofe place, as an hofpital, gaol, fhip, chamber, £sV. may be changed for frefii.

The noxious qualities of bad air have been long known, tho' not fufficiently attended to in practice ; but it is to be hoped, that the indefatigable pains taken by Dr. Hales to fet the mifchiefs arifmg from foul air in a juft light, and the eafy remedy he has propofed by the ufe of his ventilators, will at length prevail over that unaccountable floth, or obftinacy, . which, where particular interefts are not immediately con- eerned, feems to poflefs the generality of mankind, '.and which rarely allows them to give due attention to any new difcovery.

The ventilators invented by that ingenious author con- fvfts of a fquare box of any fize ; in. the middle of one fide of this box a broad partition, or -midriff is fixed by hinges, and it moves up and down by means of an iron rod, fixed at a proper diftance from the other end of the midriff, and paOing through a fmall hole in' the cover of the box. Two boxes of this kind may be employed at once, and the two iron rods may be fixed to a lever moving on a fixed center ; fo that by the alternate railing and prefling down of the lever, the midriffs are alfo alternately raifed and de- preffed, whereby thefe double bellows are at the fame time . both drawing in air, and pouring it out through apertures with valves made on the fame fide with, and placed both above and below the hinges of the midriffs. For a farther , account of this machine we refer to the author himfelf, who gives a full detail of it'; and of its manner of working. See Defcription of Ventiltitors y by Stephen Hales, D. D. Lond. 1743, 8vo.

The Doctor has fhewn the life of "his ventilators very fully. .As to fhips, in particular he obferves that the wind-fail, made ufe of at fea to introduce frefh air between decks, is far from being fumcient for that purpofe ; nor can it be ufed with equal fafety to the lick, and thofe who are deeping, by means of the ftrength of the wind which conveys the air with, too much .violence. Rut when the foul air is carried off by means of ventilators, notwithstanding the ^reat ve- locity with which they throw out the air, which they may do at the- rate of fixty tuns in a minute, yet the motion of it downwards into the hold, to fupply what is carried off, is fo very gentle, that it cannot be perceived ; becaufe the fum of all the open paffages for it through the deck exceeds the opening of the trunk of the ventilator, in fo great a proportion as 100 to 1, or more. Befides, in a calm the wind-fail can do little or no good; nor when the fhip is un- der fail, at which time the wind-fail is not ufed. And it is to be obferved, that it is not the ventilating of a fhip now and then with a wind-fail, when wind and weather ferve, that will fuffice ;. it ought to be done daily, if due regard be had to the health of the (hip's crew. The great quan- tity of rancid noxious vapours, which are inceffantly ex-

haling from a number of live human bodies, the flench that inceflkntly arifes from the bilge water, and from the hot, ftagnant, putrid air in the hold, makes it very advifeable to refrefti fo bad an air continually, either with the wind-fail, when that can be properly ufed, or elfe with ventilators^ which are intended to fupply the defects of the wind-fail. Ventilators muft alfo be of particular fervice in new fhips, which are obferved to be more unhealthy, on account of a greater quantity of fappy wreak which arifes from new tim- ber, and makes the confined air the more unwholefome. They will alfo be an effectual prefervative of horfes in tranfports, where they are fometimes fuffbeated, when in a fform there is a neceflity to fhut the hatches down. Thefe ventilators will alfo drive out of the hold of a fhip that dangerous vapour which arifes from corn, which is fo noxi- ous, that fometimes they dare not venture into the hold, till after the hatches have been opened for fome time. Ventilation will not only be of fervice to preferve feveral kinds of goods, but alfo the timbers and planks of the hold itfelf, when laid up in ordinary, as well as when in ufe, and will make the air in the hold lefs noxious, though it will ftill be offenfive to the fmell, by reafon of the bilge water- But this may be made lefs offenfive, by often letting in fweet water from the fea, and then pumping it out ; which. good practice ought to be continued, notwithftanding the ufe of the ventilators.

What is here faid of the foul air of fhips may be applied £0 that of mines, gaols, work-houfes, bai racks and hofpitals. In mines, ventilators may guard againfi the fuffocations, and other terrible accidents arifing from damps. The air of gaols has been often known to be infectious ; and we had a fatal proof of this, by the accident that happened a few years ago at the feffions at the Old-Bailey. To guard againft the like for the future, as well as to preferve the health of the pri- foners, a worthy magiftrate, in 1752, had ventilators placed in Newgate, which are wrought by a wind-mill : and in the beginning of the prefent year,- 1753, Dr. Hales gave an ac- count of the good fuccefs attending the ufe of thefe ma- chines, by a remarkable decrcafe in the ufual mortality and ftcknefs of that place.

The Doctor is alfo of opinion, that a ventilation of warm dry air from the adjoining ftove, with a cautious hand, might be of fervice to trees and plants in grecn-houfes ; where it is well known that an air full of the rancid vapours, which perfpire from the plants, is very unkindly to them, as well as the vapours from human bodies are to men. For frefh air is as neceffary to the healthy flate of vegetables, as of animals.

The larger kinds of ventilators, ufed by the Doctor, are ten feet long, five feet broad, and two feet high, in the clear within. Thofe he ufed by way of experiment on board the Captain, a feventy gun fhip, were ten feet long, four feet three inches wide, in the clear within, and thirteen inches deep ; one inch of which being occupied by the midriff, there remained a foot depth for it to rife and fall in. A ven- tilator of thefe dimenfions will, through a trunk of a foot fquare,, drive the air at the rate of twenty-five miles in art hour, which is double of. what Mariotte afTigns for the. ve- locity of a pretty ffrong wind.

But befides thefe hrge.veutilators, the Doctor made a fmaller fort, four feet in length, fixteen inches in breadth, and thir- teen inches, all in the clear within. This finalier ventilator' may be very ufeful in preferving the bread, in the bread- room of a fhip, fweet and dry. Peafe alfo, and oatmeal, which are. apt to heat and fpoi! in calks, may be preferved, ■ 'by putting them into a large bin, with a falfe bottom of hair cloth laid on bars, whereby frefh air may be blown up- wards through them with thefe fmall ventilators. Ventilators are alfo of excellent ufe for the drying of corny

. hops, and malt. Hales, lib. cit. p. 10.0, 108, 129, 151.

. Gunpowder may be thoroughly dried, by blowing air up through it by means of ventilators. Hales, ib. p. 119, feq. What advantage dry gunpowder has over that which is damp, may be feen by the experiment mentioned in the article Gunpowder, Append.

VENUS {Cycl) — Signior Bianchini has given the defcription of a globe for Venus, the principal properties of which are, that the plane of the ecliptic makes an angle of 15' with the axis, the tropics are 75 from the equator, and the polar circles only 15- from it. For a farther account of it, fee Defagidiers, E.xpcrim. Philofoph. Vol. II. p. 552, feq.

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