Page:Cyclopaedia, Chambers - Volume 1.djvu/233

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ferv,e in Minions. This Order was founded by Antoine M&rie Zacariah $ they were call'd Barnabites from the Church of St. Barnabas, at Milan,

BARNACLE, in Natural Hiftory, a little Sea- Animal, frequent among the Weftern Ifles of Scotland ; the manner of whofe Production has occafion'd fome Speculation among the Learned. The Barnacle, at firft, appears in form of a little Shell-fifh growing on old weather-beaten Timber, chiefly AJb and Fir, driven in great Quantities by the Wes- tern Ocean upon the Shores. The Shell, Sir Robert Mur- ray tells us, refembles that of a Mufcle in Colour and Con- fidence, very thin about the Edges, and about half as thick as broad, crofs'd with Sutures, &c. It hangs to the Wood by a Neck longer than the Shell, of a filmy Subftance, round and hollow, not unlike the Wind-pipe of a Chicken, by which it feems to draw its Nouri/hment from the Wood, both for its own Vegetation and that of the Animal inclo- fed. The Curiofity is, that inftead of a Fifh, which one expefb in the Shell, there is found a perfect feather'd Fowl, vulgarly call'd Solan Goofe. In a number which Sir Robert Murray open'd, he found the Sea- Fowl perfectly form'd 5 the Bill like that of a Goofe, the Eyes mark'd, the Neck, Breait, Wings, £5?c. very compleat $ the Feathers every where perfecl ; and the Feet like thofe of other Water- Fowl. He obferves, he never faw any of 'em alive ; nor does he know any body that ever did : But adds, he is credibly inform'd they have been feen as big as the Fift. The French have alfo their Barnacles, which they call Macretife, or Macroul, on the Coafts of Normandy, &c. only differing from the Scotijb, in that the one feems of the Goofe Kind, the other of the Duck Kind. Dr. T'anc. Robinfon, rejecting the popular Opinions of their being ge- nerated from rotten Woods, Fruits dropp'd into the Sea, and there metamorphos'd into Birds, &c. obferves, that the Barnacles are all oviparous, from the Anatomy of their Farts ferving to Generation, and that they are both Male and Female. Th.& French eat the Macreztfe on Fifh-Days, and throughout all Lent, taking it for a kind of Fifh. Yet Mr._R.tfjy obferves, 'tis a real Fowl j and refers it to the Species of Sea-Ducks defcrib'd by Mr. Willoughby.

BARNACLES, Horfe-Twitchers or Brakes, are Inftru- ments which Farriers apply to Horfe's Nofes when they will not ftand quietly to be /hod, blooded, &c,

BAROCO, a Term in Logick. A Syllogifm in Baroco has the firft Proposition univerfal and affirmative, but the fecond and third particular and negative ; and the middle Term the Attribute in the two firit : For Example, Every Virtue is attended with Difcretion : Some kinds of Zeal are not attended with Difcretion: therefore Jbme kinds of Zeal are not Virtues.

BAROMETER, a Machine for mcafuring the Weight of the Atmofphere, and the Variations therein, in order chiefly to determine the Changes of Weather, from the Greek @etp@-, onus, and t&lepv, menfura. The Barometer is frequently confounded with the Barofcopc, tho fomewhat improperly 5 the latter, in ftri&nefs, being a Machine that barely /hews an Alteration in the Weight of the Atmof- phere : but 'tis one thing to know that the Air is heavier at one time than at another, and another to meafure how much that Difference is 5 which is the Bufinefs of the Ba- rometer.

The Barometer is founded on the 'Torricellian Expe- riment, as 'tis call'd from its Inventor Torricelli : which is no more than a Glafs Tube fill'd with Mercury, her- metically feal'd at one End 5 the other open, and im- ■merg'd in a Bafon of Stagnant Mercury. Now, as the Weight of the Atmofphere diminishes, the Mercury in the Tube will here defcend 5 on the contrary, as it increafes, the Mercury will again afcend : the Column of Mercury fufpended in the Tube being always equal to the Weight of the incumbent Atmofphere 5 as is Shewn under the Word Torricellian.

ttke Mcchanifm of the Barometer is as follows.

A Glafs Tube A B, Plate 'Pneumaticks, Fig. 1. herme- tically feal'd in A, having its Diameter about \^ of an Inch, and its Length at leaft 31 Inches, is fill'd with Mercury fo juftly, as not to have any Air over it, nor any Bubbles adhering to the Sides of the Tube 5 which is beft done by means of a Glafs Funnel, with a capil- lary Tube. The Orifice of the Tube, fill'd after this manner, fo as to overflow, is clofcly prefs'd by the Finger, fo as to exclude any Air between it and the Mercury, and thus immerg'd in a wooden Veffel, of a convenient Diameter; fo, however, as not to touch the Bottom : At the Diftance of 28 Inches from the Surface of the Mer- cury, are fix'd two Plates, C E and DF, divided into two Inches, and thefe again Subdivided into any Number of fmal- ler Parts : Laftly, the Tube is inclofed in a wooden Frame, to prevent its being broke 5 and the Bafon, tho open to the Air, fecured from Duftj and the Barometer is compleat.

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Many Attempts have been made to render the Changes in the "Barometer more fenfible, and fo to meafure the At- mofphere more accurately ; which has given Rife to a great Number of Barometers of different Structures. Hence comes the Wheel "Barometer, "Diagonal Barometer, Hori- zontal Barometer, 'Pendant Barometer, &c. of each where- of in their turns.

Des Cartes, and after him Huygens, ufed a Tube A B, Fig, 2. having a Cylindrick Veffel CD; one half of which Veffel, together with the upper Part of the Tube, were fill'd with Water ; the other half of the Veffel, and the lower Part of the Tube, with Mercury : But here, tho the Column fufpended was larger, and consequently the Variation great- er, yet the Air imprifon'd in the Water getting loofe by degrees, fill'd the void Space in the top, and fo ruin'd the Machine. He then bethought himfelf of placing the Mer- cury a top, and the Water at bottom, in the manner follow- ing : AD G, Fig. 3. is a bent Tube hermetically feal'd in A, and open in G ; the cylindrick Veffels B C and F E are equal, and about 29 Inches a-part ; the Diameter of the Tube is about a Line, that of each Veffel 1 5 Lines, and the Depth of the Veffels about 10 ; the Tube is fill'd with Mercury (the common Barometer Handing about 29 Inches) which will be fufpended between the middle of the Veffel F E, and that of the Veffel BC; the remaining Space to A, being void both of Mercury and Air: Laflly, common Water, ting'd with a fixth Part of Aqua Regis, to prevent its freezing, is pour'd into the Tube F G, till it rifes a Foot above the Mercury in D F. When, then, the Mercury rifing above the Level of that contain'd in FE, through the Tube A D, becomes a Balance to the Weight of the Atmofphere ; as the Atmofphere increafes, the Column of Mercury will increafe, consequently the Water will defcend ; as the At- mofphere again grows lighter, the Column of Mercury will defcend, and the Water afcend. This Barometer there- fore, which is the fame with that of Dr. Hook, will difco- ver much minuter Alterations in the Ait than the common one : for, inftead of two Inches, the Fluid will here vary two Foot ; and by enlarging the Diameters of the Cylinders, that Variation may be Hill increas'd; but it has this Incon- venience, that the Water will evaporate, and fo render the Alterations precarious ; tho the Evaporation be, in fome meafure, prevented by a Drop of Oil of fweet Almonds fwimming a-top. On account of this Defect, others have had recourfe to a

Horizontal, or Reel 'angular Barometer, A B C D, Fig. 4. the Tube whereof is bent, in form of a Square B C D 5 a-top of its perpendicular Leg it is join'd to a Veffel or Cistern A B ; and its Variation accounted on the Ho- rizontal Leg C D. Now here the Interval, or Space of Variation, may be made of any Extent at pleasure, and fo the minuteft Change in the Air become fenfible. For the Diameter of the Tube C D being given, 'tis eafy to find the Diameter of the Veffel A B, fo as that the Scale of Defcent in the Tube D C fhall have any given Pro- portion to the Scale of Afcent in the Veffel A B ; the Rule being, that the Diameter of the Veffel is to that of the Tube in a fubduplicate reciprocal Ratio of their Scales. The Diameters then of CD and A B being given, together with the Scale or Afcent of the Mercury in the Veffel, the Scale of Mercury in the Tube is found thus ; as the Square of the Diameter of the Tube is to the Square of the Dia- meter of the Veffel, fo, reciprocally, is the Scale of Mer- cury in the Veffel to the Scale of Mercury in the Tube.

This and the preceding Contrivance of Huygens, are founded on a Theorem in Hydroftaticks, viz. that Fluids having the fame Safe, gravitate according to their perpen- dicular Altittide, not according to the Qtiantity of their Matter ; whence the fame Weight of the Atmofphere sup- ports the Quicksilver that fills the Tube A D and the Cif- tern B, as would fupport the Mercury in the Tube alone. See Hydroftaticks.

This last however, with its Virtues, has great Defects ; for, by reafon of the Attraction between the Parts of the Glafs and of the Mercury, (which Dr. Jurin has ihewn to be considerable) the Length of the Scale, (confequently the Quantity of Motion) and the Attrition against its Sides, especially in hidden Rifes and Detents, the Mercury breaks, fome Parts of it are left behind, and the Equability of its Rife and Fall ruin'd. Some therefore prefer the

"Diagonal Barometer, where the Space of Variation is considerably larger than in the common one, and yet the Rife and Fall more regular than in the others. The Foun- dation of the DiagonalBarometer is this ; that in a Torricel- lian Tube A B, Fig. 5. inclined at any Angle to the Horizon, the Cylinder of Mercury equivalent to the Weight of the Atmofphere, is to a Cylinder of Mercury, equivalent to the fame placed in a vertical Tube, as the Length of the Tube A B to the perpendicular Height B C. Hence, if the Height BC be iubtriple, fubquadruple, &c. of the Length of the Tube, the Changes in the Diagonal Barometer will

be