BAG 



B A C 



fnch as liave been ilTuedbya juftice of the peace in one 

 county, by a juftice of the peace in another county, which 

 \s neceffary bf-fore they can be executed there. Tliis 

 yraftice, which had lo'n^ prevailed witiiout law, is au- 

 ihorifed by llatutes 23 Geo. II. c. 26. and 24 Geo. II. 

 C.55. And now, by ftatutc 13 Geo. III. c. 31. any 

 V arrant for apprehending an Erglifh offender, who may 

 have efcaped into Scotland, and vice vsr/u, may be endoiled 

 and executed l)y the local magiftrates, and the offender con- 

 veyed back to that part of the united kingdom, in which 

 fuch oHeiice was committed. 



Back-AWj-. See Nail. 



BiiCK-Ptiiii.'itig, is iifed by fome for the art of parting of 

 prints and other dtfifrns crf-glafs. 



The art conlilh chiefly in laying the print upon a piece 

 of crown-glafs, of fnch a fiv.e as i'lts the print. In order to 

 do this, the print mull be fotiked in clean water for forty- 

 eight hours, if it be on very llrong, clofc, and hard gum- 

 med paper ; but if on a foft, fpongy paper, two hours 

 will fometimcs be fufficient. The piftuie, being well 

 foaked, muft be laid between four (beets of paper, two 

 over and two under it, that the moifture may be drawn 

 out of it. Inllead of foaking the print, it may be rolled 

 up and boiled for about two hours, more or lefs, according 

 to the quality of the paper, in water ; and this mode 

 ■will anfwer the purpofe as well as foaking it. In the mei'n 

 ■while, let the glafs upon which th.e print is to be laid be 

 warmed at the fire ; then with a hog's-hair brufh dipped 

 in melted Strafburg turpentine, fpread the turpentine 

 fmoothly and evenly on the glafs. Then lay the print upon 

 the glafs, rubbing it gently from one end to the other, that 

 it may lie clofe. With the finger, rub off the paper from 

 the back fide of the print, till nothing can be feen but the 

 print, like a thin film left upon the glafs, and fct it afide 

 to dry. When it is dry, varnifh it over with fome white 

 tranfparent varnilh, that the print may be feen through 

 it, which is now fit for painting. 



Having prepared a variety of oil colours, which muft be 

 ground very tine, and tempered vei-y ft iff, lay fuch colours 

 on the tranfparent print as each particular part requires, 

 the mailer-lines of the print guiding the pencil ; and thus 

 tach colour will appear fair to the eye on the other fide of 

 the glafs, and look almoft as well as a painted piece, if it be 

 done neatly. The Ihadows of the print are generally fuf- 

 ficient for the (hadow of every colour; but if it be defired 

 to give a (hadow by the pencil, the (haJows ibould be laid 

 on firll, and the other colours afterward. The chief care 

 to be ufed in this part of the work, is that of laying the 

 colours on thick enough, that they may be ftruck plainly 

 through the glafs. 



3^-CK-Rivcr, in Gnogmphy. See Baltimore. 



BACKS, among dealers in leatlier, denote the thickeft 

 and bell tanned hides, ufed chiefly for foks of (hoes. See 



Bl'TTS. 



Backs of a H':p. See Hip. 



B\C¥.JlaJf, in Nav'gati'jii, an inftrument, by the French 

 called the En^lif} quadrant. It was invented by captain 

 Davis, about the ye^r i5yo; and is of good ufe in taking 

 the fun's altitude at fea. It confills of three vanes, A, B, 

 and C, and of two concentric arches {Plate 1. Navigation, 

 fg. 2.) ; the vane at A, culled the horizon-vane; that at 

 B, '.he (hade-vane ; and that at C, the Jight-vane. The 

 lefT arch B (or ED) is of 60 degrees, and that of C (or 

 FG) of 30 degrees. 



T. ufe the hack.faff. The (hadow-vane B is fet upon the 

 60 arc h, to an even de^rr-.- of I'oir.c latitude, Ljfs by 10 or 

 Jj dejjiecs than )ou jud^jC the complement of the fun's al- 



titude will be ; the horizon vane is put on st A, and the 

 litfht-vane on the 30 arch FG : the obferver's back being 

 then turned to the fun (whence the name of hack flag, or 

 bachquadmnt'), he lifts up the inftrument, and looks through 

 the iiglit-vanc, raifing or (ailing the quadrant, till the (hadow 

 of the upper edge of the Ihade-vane (all on the upper edge 

 of the flit of the horizon vane ; and then if he can fee the 

 horizon througli the laid (lit, the obfervation is well made ; 

 but if the fea appear inllead of the horizon, the fight vane 

 muft be moved lower towards F ; if the (ley appear, it muft 

 be moved upward towards G, and thus tried till it comes 

 right : then he obferves how many degrees and minutes are 

 cut by that edge of the figtit-vane which anfwers to the 

 fight-hole, and to them adds the degrees cut by the upper 

 edge of the ftiade-vane : the fum is the fun's diltance from 

 the zenith, or the complement of his altitude. To find the 

 fun's meridian, or greateil altitude on any day, continue 

 the obfervation as long as the altitude is found to increafe, 

 ■which you will perceive by the appearance of the fea, in- 

 llead of the horizon, removing the fight-vane lower ; but 

 when you perceive the fl<y appear inllead of the horizon, 

 the altitude is diniinilhed ; therefore, defill from farther ob- 

 fervation at that time, and add the degrees upon the 60 

 arch to the degrees and minutes upon the 30 areh, and the 

 fum is the zenith dittance, or co-altitude of the iun's upper 

 limb. 



And becaufe it is the zenith diftance, or co-altitude of 

 the upper limb of the fun, and not the centre, that is given 

 by the q.;adrant, in oblerving by the upper edge of the 

 (hade-vane, add 16 minutes, the fun's femidiameter, to that 

 which is produced by your oblervation, and the fum is the 

 true zenith diftance of the fun's centre. If you obferve by 

 the lower part of the (hadow of the (hade-vane, then the 

 lower limb of the fun gives the (hado-.v ; and, therefore, 

 you muft fubtradl 16 minutes from what the inftrument 

 gives : but confidering the height of the obferver above the 

 furface of the fea, which is cemmonly between 16 and 20 

 feet, you may take 5 or 6 minutes from the 16 minutes, 

 and make the allowance but of 10 minutes or 12 minutes, 

 to be added inllead ot 16 minutes. 



Mr. FlamfteeJ contrived a glafs lens, or double convex, 

 to be plactd in the middle of tiie Ihadc-vane, which makes 

 a final] bright Ipot on the flit of the horizon-vane, inltead 

 of the (hade ; which is a great improvemtnt, it the glafs be 

 truly made ; lor, by this means, the inftrument may be 

 ufed in hazy weather, and a much more accurate oblerva- 

 tion made in clear weather than could be by the (hadow. 



The theory of this quadiant is very iiiuUigible : for the 

 line AC being horizontal, the arc _/GC is equal to the 

 height of the lun above the horizon ; but this arc _/"GC is 

 equal to the fum of the arcs BE + GC ; ai.d tjie arc if^ 

 =; 90'' =; the altitude and zenith diftance taken together ; 

 coniequently the Zenith Oillancc ;;=. the arcs _/</ -f- CF = 

 DB i- CF. 



When the horizon is obfcured by hazy weather, Davis's 

 quadrant is of no uie j a:iu this often octafions dillrefling 

 conlequences. ^lea^]S have therefore been louglit for to 

 remedy this defedt. Mr. Hadlcy has recommei ded and de- 

 Icribed a (pirit level for this purpofe. Mr. Leigh propoled 

 to fix a water-Lvel to the qujdiant ; and he has likewife 

 given the defcription and uie ol an apparatus to be E-Ued to 

 this inftrument, eonfilluig ot a meicuriai level, >■• nich he 

 prefers, with realon, to a water-level. Set i lul. Tranf. 

 N"'430, &c. or Martyn's Abr. vol. vr.i. p^j7,36o,&c. 



It h<!S been obferved, that cue ^r^ui objection againft 

 thi^ in!tr;uneiit is the tieiui le and lime lult in (lieiing the 

 li^ht-viiiie upwaiU or Uowuvvaid; winch louietimes cannot 



couvemently 



