LOO 



LOO 



Zvr to! touch the wint! ! havt n cars tf the he-latch I All 

 which words fignify much t!ie fame thing, and bid the man 

 at the helm to keep the fliip near the wind. 



LooF ofajhlp, denotes the after-unrt of a (hip's bow ; or 

 tliat part of hpr fide forwurd wlnre the planks begin to 

 be incurvated into an arch, as they approach the ftem. 

 Hence, the guns which lie here are called loof-pieces. 



L.oot'-hooi, in a Ship, a tackle with two hooks to it, one 

 of which is to hitch into the crenglc of tlie main and fore- 

 fail, and the other is to hitch into a certain (trap, which is 

 fpliced into the cliefs-trce, :ind fo down the fail. Its ufe is 

 to fuccour the tackles in a large fail, that all the ftrefs may 

 not bear upon the tack. Sometimes alfo it is ufcd when the 

 tack is to be feized the furer. 



Loop-/<7i,-i/c, or 'Lvi'V-taci/e, a large tackle, larger than 

 the jigger-tackle, but fmaller than thofe which hoill the 

 heavier materials into and out of the vefl'el, fuch as the main 

 and fore tackles, the (lay and quar-ter tackles, &c. ferving 

 to lift all the fmall weights in or out of the (hip, and other- 

 wife varioufly employed as occalioii requires. 



Loop, or Loop, a corn-meafure at Riga, equal to 397S 

 cubic inches ; of which 4324 arc equal to ten Englilli quar- 

 ters. 



LOOHOGGO.in Geography, one of the fmaller Friendly 

 ijftands, furrounded by a reef of rock.^. S. lat. 19^ 41'. 

 E. long. 185° 36'. 



LOOJAMA, a town on the E. coaft of the ifland of 

 Timor. S. lat. 8' 27'. E. long. 126 ' 18'. 



LOOKING Glass, a plain polilhed glafs fpeculum, or 

 mirror, to one fide of which a plate of tin-foil is made to 

 adhere by means of quickfilver ; which being impervious to 

 the light, reflefts its rays, and fo exhibits the images of 

 objcdls placed before it. 



In confequence of this conllruftion, the looking-glafs 

 makes a double refleftion of every objeft, viz. one from 

 the upper furface, which is the weakeit, and another from 

 the under furface, which is contiguous to the tin-foil. 

 When a perfon ftands juft before the glafs, the two reflec- 

 tions coincide, and he perceives one image ; but if he ftands 

 oblique, as at A, (Plate IX. Optics, fg. 10.) and views the 

 reflection D, of an objeft B C, lituated on the other fide, 

 he will then perceive two images, -ji-z^ one caufed by the 

 upper, and the other caufed by the lower furface of the 

 glafs E F. If the objeft B C be very luminous, fuch as a 

 lighted candle, then the eye at A will perceive a great fuc- 

 ceffion of candles at D, gradually decreafinj; in fplendour ; 

 the caufe ot which phenomenon is, that the ftrong relleftion 

 from the under furface of the glafs is again refiefted from 

 the upper furface, and this again by the lower, &c. 



The theory of looking-glaflcs, and the laws whereby they 

 give the appearance of bodies, fee under Mirkok. 



L.00KiSG-glnJps, the manner of grinding and preparing, is as 

 follows: —a plate of glafs is fixed to a horizontal table of 

 free-itone or wood, of about tlie fanvj fize, and cemented 

 to it by Paris plalter ; and to another Ien"er table is fixed in 

 •the fame manner another plate. Over the firft plate is 

 fprinkled fine fand and water, in a fufficient quantity for the 

 grinding, and the fecond or lefs plate is laid on it ; and thr.s 

 worked this way and that way, till each has planed the 

 other's furface. Thefe plates are made to rub againii: each 

 other evenly and fteadily by a kind of hand-mill, the wheel 

 of which is wrought by a man, or if the plates be large by 

 .two men, who regulate the preffure as they think proper. 

 As they begin to become fmoother, finer fand is fucccflively 

 lifed. When one fide of the plate is finidied, the plafter 

 that ccmeated :t is picked off, and the plate turned, fo 



that the other fide may be ground in the fame manner. To- 

 wards the clofe of the operation of grinding, the preffure is 

 incivafed by loading the upper plates with flat ftones of 

 different tliickneffcs. This procels falls about three days, 

 and it is of great importance that the fin faces fhould be ptr- 

 feftly flat and parallel, which is aetcrmiiied by the ruler and 

 plumb-line. In order to complete this procefs, emery of 

 different fineneflcs is ufed, and great care is taken iu fcpa- 

 rating and forting them, 'i'his is done by putting into a 

 vefiel of water a quantity of rough emery, and well ilirririg 

 it ; the coarfeft particles will fink to the bottom, and the 

 finer will be held fufpendcd for fome time by the fuper- 

 iiatant liquor. This liquor is poured off, and after fome 

 time, about 20 minutes, the finer particles will fiibfide. 

 More water is then added to the vellel, and- the emery flirrcd 

 again; and after remaining at reil about 15 minutes, the 

 fiipernatant liquor is poured ofi ; and this by red furniflies 

 an emerv of the fecond degree ot fiiienefs. The fame opera- 

 tion is repeated twice more at the different intervals of about 

 five minutes and half a minute ; by which two other forts 

 are obtained. The wet emery obtained from all thefe 

 liquors is feparably heated over a ftove to evaporate the 

 water, and when nearly dry, is made up into balls tor the 

 further operation. The plates are then ground on both 

 fides with two or three emcrys, beginning with the coarfeft, 

 and finilhed with great care. They are how perfeftly 

 even, and the fcratches, which after the firll operation 

 remained and rendered them almofl opaque, difappear. (See 

 Grindjn'G.) For the method of poliihing looking-glaffes 

 and mirrors, we refer to the article Polisjilng. 



The plates being polilhed, a thin blotting paper is fpread 

 on a table or marble flab ; and fprinkled with fine powdered 

 chalk ; and this done, over the paper is laid a thin lamina 

 or leaf of tin, on which is poured mercury, which Is to be 

 equally diftributcd over the leaf, with a hare's foot or cot- 

 ton. Over the leaf is laid a very thin fmooth paper, of 

 which the kind called fan-paper'fis bell, and over that the 

 glafs plate. With the left hand the glafs-plate is preffed 

 down, and with the right the paper is gently drawn out ; 

 which done, the plate is covered with a thicker pap.r, and 

 loaden with a greater weight, that the fuperfluous mercury 

 may be driven out, and the tin adhere more clolely to the 

 glafs. When it is dried, the weight is removed, and the 

 looking-glafs is complete. 



Some ufe an ounce of mercury with half an ounce of 

 marcafite or bifmuth, melted by the fire ; and left the mer- 

 cury evaporate in fmoke, pour it into cold water; and 

 when cold, fqueezc it through a cloth or leather. Some 

 alfo add a quarter of an ounce of lead and tin to the mar- 

 cafite, that the glafs may dry the fooner. For more par- 

 ticular direftions in the conduft of this operation, fee 



SlI-VEKING. 



In the Phil. Tranf. N" 24 J, we have a method oi foliating 

 (fee Foliating) globe lookiiig-giaffes, communicated by 

 fir R. Southwell. The mixture is of quickfilver and bif- 

 muth, of each three ounces, and tin and lead, of each half 

 an ounce ; to the lall throw in the marcafite, and afterwards 

 the quickfilver ; ftir them well together over the fire ; but 

 they mull be taken off, and be towards cooling before the 

 quickfilver be pnt to them. When the mixture is ufed, 

 the glafs (liould be well heated, and very dry ; but it will 

 do alfo when it is cold, though bell when the glafs is 

 heated. 



Mr. Boyle's method, which he prefers to any which he 

 ever met with in prist, is tliis : take tin and lead, of each 

 on€ part, niclt ihem together, aud immediately add of 



good 



