J AC 



404 



JAC 



when g soft is required, as iujet, to dis- 

 tinguish from get. 



JAC'ANAS, a genus of birds. Order 

 Grallatoria. Distinguished by having four 

 very long toes, separated down to their 

 root, the nails of which are extremely 

 long' and pointed, a circumstance which 

 has procured for them the vernacular 

 name of surgeons. They are noisy and 

 quarrelsome birds, and inhabit marshes 

 in hot climates, where they walk with 

 great facility, by means of their long 



~JACA-TREE, a name of the bread-fruit- 

 tree of the East Indies. 

 See ARTOCARPCS. 



JA'CINTH, )SeeH?- 



JACIN'THUS ) ACINTH 

 and HYACINTHCS. 



JACK. 1. In mecha- 

 nics, an instrument in 

 common use for raising 

 great weights, being a 

 powerful combination 

 at teeth and pinions, 

 and the whole inclosed 

 in a box. The power 

 is applied by a winch 

 or handle. The figure 

 represents the machine 

 without the frame. 

 The kitchen-jack is a 

 machine in which the JACK. 



descent of a weight is 

 made to turn a spit. The common 

 worm-jack is shown in the figure. The 



KITCHEN -JACK. 



smoke-jack is another contrivance for the 

 same purpose as the common worm or 

 kitchen -jack, but acting, not by a weight, 

 but. by means of the smoke passing up 

 the chimney, which striking against a set 

 of oblique vanes , fixed to a vertical spindle , 

 causes it to revolve with great rapidity. 

 This motion is conveyed to the spit by 

 means of a smal wheel, which works into 

 auotiier small wheel placed on the end of 



a horizontal spindle, having a pulley at 

 the other end, over which passes the chain 



which works the spit. The name jack it 

 very commonly applied to vibrating levers 

 in variouskinds of machinery, as in stock- 

 ing-frames, &c. 2. In navigation, a sort 



of flag or colours displayed from the bow- 

 sprit. In the navy the j ack is a small union 

 flag, but in merchant ships the union is 



bordered with red. 3. Tn ichthyology, the 



young pike, Esox Indus. 4. In botany, 



the Isjaca, a species of bread-fruit- tree. 



JACK'AL, corrupted from chacal, a canine 

 animal, the Cams aurevs, Lin., found in 

 the Indies, and the environs of the Cas- 

 pian Sea, and as far as in Guinea. 



JACK ARCH, an arch of the thickness of 

 only one brick. 



JACK'-BACK, the largest jack of the 

 brewer. 



JACK'BLOCK, a block attached to the top- 

 gallant-tie of a ship, to swing up or to 

 strike the sail. 



JACK'DAW. In ornithology , the Corvus mo- 

 nedula, Lin. , is the jackdaw, a well-known 

 bird ; and the Gracula guiscala is named, 

 from its colour, the purple jackdaw. 



JACK'FLAG, a flag hoisted at the sprit- 

 sail top-mast-head. 



JACK-IN-THE-BOX, 1. Alarge wooden solid 

 screw, turning in a hollow one, which 

 forms the upper part of a strong wooden 

 box, shaped like the frustrum of a pyra- 

 mid. It is wrought by means of levers 

 passing through holes in it, as a press in 



packing, &c. 2. The popular name of 



a genus of arborescent plants. 



JACK-OF-HILTON, a vulgar name for an 

 aeolipyle. 



