JAC

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J A C

which is the distance or space the power moves through in one re-volution of the handle ; but as the pinion of the handle has butfour leaves, and the wheel Q suppose twenty teeth, or five limesthe number; therefore to make one revolution of the wheel Q, itrequires five turns of the handle, in which case it passes throughfive times forty-four, or two hundred and twenty inches ; but thewheel having a pinion R of three leaves, these will raise the rackthree teeth, or one inch, in the same space. Hence, then, thehandle or power moving two hundred and twenty times as fast asthe weight, will raise or balance a weight of two hundred andtwenty times its own energy. And if this is the hand of a manwho can sustain fifty pounds weight, he will, by the help of thisjack, be able to raise or sustain a weight or force of eleven thou-sand pounds, or about five tons weight. This machine is some-times open behind, from the bottom almost up to the wheel Q, toiet the lower claw, which in that case is turned up as at B, draw upany weight. When the weight is drawn or pushed sufficiently high,it is kept from going back by hanging the end of the hook S, fixed to astaple, over the curved part of the handle at h. Mr. Mocock, ofSouthwark, obtained a premium of twenty guineas from the Societyof Arts, for bis contrivance to prevent a jack from taking a retro-grade course whenever the weight by any accidental circumstanceover-balanced the power. The improved jack only differs fromthose in common use in this respect, that it lias a pall or dock, andratchet, applied in such manner as to stop the motion of the ma-chine as soon as it begins to run back again. As the difference inthe mechanism is very tvitling, the improvement may be easily-applied to any common jack already made, and indeed ought notto he omitted.

Jack is also the name of a well-known engine, in the kitchen,used for turning a spit. Here the weight is" the power applied,acting by a set of pulleys ; the friction of the parts, and .the weightwith which the spit is charged, are the forces to be overcome ; anda steady uniform motion is maintained by means of a fly. ABC,fig. 11, represents the barrel round which the cord QR is wound;KL the main wheel, commonly containing sixty teeth; N theworm-wheel of about thirty teeth' cut obliquely ; ’LM the pinion,ot about fifteen ; O the worm or endless screw, consisting of twospiral threads, making an angle of sixty or seventy degrees with itsaxis; X the stud, and Z the loop of the worm-spindle ; P a heavywheel or fly, connected with the spindle of the endless screw tomake the motion uniform ; DG the struck-wheel fixed to the axisFD; S, S, S, are holes in the frame, by which it may be nailed toa board, and thence to any wall, the end D being permitted to passthrough it; Ill the handle going upon the axis F.T, to wind upthe weight when it has run down. R is a box of fixed pullevs,and V a corresponding one of moveable pullevs carrying theweight. The axis FT is fixed in the barrel AC, which axis beinghollow, both it and the barrel turn round upon the axis FD, whichis fixed to the wheel KL, when it turns in the order BTA ; butcannot turn the contrary way, by reason of a catch nailed to theend AB, which lays hold of the cross-bars in the wheel LK. Theweight, by means ot the cord QR, in consequence of its descent,carries about the barrel AB, which by the action of the catch carlies the wheel KL, and this moves the pinion LM and wheel N,the latter moving the worm O and (he fly P. Also the wheel LMcarries the axis FD with the wheel DO, which carries the cord orchain that goes about tire wheel or pulley at the head of the spit.But when the handle II gives motion to the axis in a contrary or-der to that given by the weight, the catch is depre-sed ; so'thatalthough the barrel BC moves and winds the cord upon it, thewheel DG continues at rest. The time which the jack continuesin motion depends upon the number of pulleys at R and V : andas these increase or decrease, so must the weight which communi-«ates the motion, in order to perform the same work in the sametime.

Jack, Smoke, is an engine used for the same purpose as thecommon jack ; and is so called from its beiug moved by means ofthe smoke, or rarilied air, ascending the chinmev, and strikingagainst the sails of the horizontal wheel AB, fig. 10, which bein”inclined to the horizon is moved about the axis'of the wheel, to”getlier with the pinion C, which carries the wheels D and K ; ’andE carries the chain F, which turns tiie spit. The wheel AB shouldbe placed in the narrow part of the chimney, where the motion ofthe smoke is swiftest, and where also the greatest part of it muststrike upon the sails. The force of this machine depends upon

the draught of the chimney, and the strength of the fire. Smoke-jacks are sometimes moved by means of spiral flyers coiling abouta vertical axle ; and at other times by a vertical wheel with sailslike the float-boards of a mill; but the above is the more custom-ary construction.

Jack, in sea-language, a flag, displayed from a mast erected onthe outer end of a ship’s bowsprit. In the British navy the jack isa small union flag; but in merchant ships this union is borderedwith a red field. See Union.

Jack is used also for a great leathern pitcher to carry drink in.

Jack, Smoke. See Smoke-Jack.

Jack-by-the-IIedge. See Ervsimum.

Jack Flag, in a ship, a flag hoisted up at the sprit-sail top-masthead.

Jack-in-a-box. See Hernandia.

Jack-with-a-i.antern, an ignis fatuus.

JACKAL, in zoology. See Canis.

JACKDAW. See Coitvus. 'These birds are very mischiev-ous to the farmer and gardener. The following useful method ofdestroying them by a kind of spring is much used. A stake aboutlive feet long is driven into the. ground, and made so fast that itcannot move, and so sharp in the point that the bird cannot settleupon it. Within a fool ot the top a hole is bored through it, ofthree quarters of an inch diameter; through this hole is put a stickeight inches long; then a horse-hair noose is made fast to a thinhazel wand, and this brought up to the place where the short stickis placed, and carried with it through the hole, the remainder be-ing left open under that stick. 'The other end of the hazel-rod isput through a hole in the stake near the ground, and fastenedIbere. 'The stake being planted among the jackdaw’s food, lie isnhturally led to settle on it: but finding the point too sharp, hedescends to the little cross-stick, which sinks with his weight, andthe noose holds him fast by the leg.

JACKSON, Port, a port and bay of New South Wales , onthe E. coast of New Holland, 9 miles N. of Botany Bay .

JACM EL, a sea-port of Hispaniola , on the neck ot the S. pe-ninsula.

JACOB, [31J3JJ, Ileb. i. e. a supplantcr,] the son of Isaac andRebekah, was born A. M. 21 OS, and B. C. 1836. 'The history ofthis patriarch is recorded in Genesis, xxv.—I. lie died in Egypt in the 147th year of his age, and was honourably interred in Abra-ham ’s burying-place, near Hebron.

Jacob, "Giles, an eminent lawyer, born at Romsey in Soulh-amptonshire, in 1686 . He is principally known for his Law Dic-tionary in one vol. folio, which has been often printed, lie alsowrote two dramatic pieces; and a Poetical Register, containingthe lives and characters of English dramatic poets, lie died in1 / 4-h*

Jacob Ben IIajim, a rabbi famous for the collection of theMasora in 1515; together with the text of the bible, the Chaldaicparaphrase, and Rabbinical commentaries.

Jacob Ben Naphthali, a famous rabbi of the fifth century:he was one of the principal Masorels, and bred at the school of i i'berias in Palestine with Ben Aser. The invention of (he vowel-points, and of accents to facilitate the reading of the Hebrew , areascribed to these two rabbis: and said to have been done in an as-sembly of the Jews held at Tiberias, A. D. 476.

JACOBINS , or the JACOBINE CLUB, in modern historyand politics, a political party in France , who cut a very conspicu-ous figure in the commencement ot the Trench revolution; an"were so called from (heir meeting in the hall of the.Jacobin Friar 5at Paris. Many of them were members of the Constituent N a 'lional Assembly of Fiance, and many more were deputies lo tb®different conventions which succeeded if. 'They are represent^as having been determined enemies to monarchy, aristocracy, an"the Christian religion ; as “ outrageously democratical, and'faiiati'cally impious.” The origin of tills sect or party has been ascribed toM.'Voilaire, “who, daring (says Dr. Gleig,) to be jealous of b> 5God , and being weary, as he said himself, of hearing people t e "peat, that twelve men were sufficient to establish Christianity ^/ 1 :’!solved to prove that one might be sufficient to overthrow- it. a*n ^of this project, he swore, before 1730, to dedicate Ids life to its a cccmpiishmenl; and for some time he flattered himself, that* 1 'should enjoy alone the glory of destroying the Christian religi° n Jlie found, however, that associates would be necessary; and ft° n cHie numerous tribe of his admirers and disciples, he eh 0 ”

I •' D'Aki» belt