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plain, that the power upon the whole wedge (where the 

 whole back is double the half back ) muft be to tlie refiftance 

 againft both its fides, as the thicknefs of the whole back is 

 to the length of both the fides, fuppofing the wedge at the 

 bottom of the cleft ; or as the thicknefs of the whole back 

 to the length of both fides of the cleft, when the wood 

 fplits at any diftance before the wedge. For when the 

 wedge is driven quite into the wood, and the wood fplits at 

 ever fo fmall a diftance before its edge, the top of the 

 wedge then becomes the afting part, becaufe the wood does 

 not touch it any where elfe. And fince the bottom of the 

 cleft muft be confidered as that part where the whole ftick- 

 age or refiftance is accumulated, it is plain from the nature 

 of the lever, that the farther the power adls from the refift- 

 ance, the greater is the advantage. 



Some writers have, indeed, advanced, that the power of 

 the wedge is to the refiftance to be overcome, as the thick- 

 nefs of the back of the wedge is to the length only of one 

 of its fides ; but this, fays Mr. Fergufon, feems very ftrange; 

 for, if we fuppofe A B [Jig- 4. ) to be a ftrong inflexible 

 bar of wood or iron fixed into the ground at C B, and D 

 and E to be two blocks of marble lying on the ground on 

 oppofite fides of the bar ; it is evident that the block D 

 may be feparated from the bar to the diftance d equal 

 to a b, by driving the inclined plane or half-wedge ab 

 down between them ; and the block E may be feparated to 

 an equal diftance on the other fide, in like manner, by the 

 half-wedge c d 0. But the power impelling each half-wedge 

 will be to the refiftance of the block againft its fide, as the 

 thicknefs of that half-wedge is to the length of its afting 

 fide. Therefore the power to drive both the half-wedges is 

 to the refiftances, as both the half backs are to the length 

 of both the afting fides, or as half tlie thicknefs of the 

 whole back is to the length of either fide. And, if the bar 

 be taken away, the blocks put clofe together, and the 

 two half-wedges joined to make one ; it will require as much 

 force to drive it down between the blocks, as is equal to 

 the fum of the feparate powers afting upon the half-wedges 

 when the bar was between them. Fergufon's Left. p. 40, 

 &c. 4to. See alfo Defag. Exp. Phil. vol. i. p. 107, &c. 



Mr. Ludlam, in an EfTay on the Power of the Wedge, 

 printed in 1770, propofes, with a particular view to the 

 machines defcribed by S'Gravcfande, Defaguliers, and Fer- 

 gufon, for eftimating the power of the wedge, to determine 

 this power, when two equal forces aft on the fides of an 

 ifofceles triangle in direftions parallel to the back but op- 

 pofite to each other, and are fuftained by a third force aft- 

 ing perpendicularly on the back of the wedge. For this 

 purpofe, let A B C (Jig- 5-) be an ifofceles wedge, whofe 

 angular point is C, fides A C and B C, back A B, and 

 perpendicular height H C : let F E reprefent the quantity 

 and direftion of the force applied to one of the fides ; this 

 may be refolved into two other forces FD and D E, the 

 former parallel and the latter perpendicular to the fide A C ; 

 and tlie obhque force F E will have juft the fame effett 

 upon the wedge as a lefs perpendicular force D E ; the 

 former being to the latter as A C is to H C. But tliis laft 

 perpendicular force on the fide A C is to that on the back 

 which balances it as A C is to A H ; whence compounding 

 thefe ratios, the oblique force againft one fide of the wedge 

 JB to the perpendicular force on the back which balances it, 

 as A C^ is to A H x H C. The oblique force/c on the 

 other fide of the wedge, being equal to F E, will require 

 another perpendicular force on the back to balance it equal 

 to the former perpendicular force ; whence the whole force 

 on both fides of the wedge is to the whole force on the 

 back as A C Ms to A H x H C ; or as the fquare of the 



Vol,. XXXVIII. 



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fide of the wedge to the reftangle under half the back and 

 the perpendicular height. 



For other methods of efl iiating the eff"eft of the wedge 

 in various cafes, fee Mechanical Powers. 



The wedge is a very great mechanical power, fince not 

 only wood but even rocks can be fpht by it ; which it 

 would be impofllble to efFeft by the lever, wheel and axle 

 or pulley ; for the force of the blow or ftroke, (hakes the 

 cohering parts, and thereby makes them feparate the more 

 eafily. 



To the wedge may be referred all edge-tools, and inftru- 

 nients which have a fharp point, in order to cut, cleave, (lit, 

 chop, pierce, bore, or the like ; asr knives, hatchets, fwords, 

 bodkins, &c. 



Wedge, in Ship-Butld'mg, a triangular fohd made of 

 wood or iron. It is one of the mechanic powers, the moft 

 fimple, and of the greateft force. 



WEDGE Island, in Geography, a fmall ifland in the 

 North Pacific ocean, near the E. coaft of the Prince of 

 Wales's Archipelago, in the Duke of Clarence's Strait. 

 N. lat. 55° 8'. E. long. 228° 20'. 



WEDGES, in Agriculture, are a fort of levers or dif- 

 tending powers that are of great ufe to the farmer on many 

 occafions, as in tearing and fphtting wood of all forts, 

 the roots of trees in taking them out of the ground, ftones, 

 and many other forts of hard materials. About farm- 

 houfes of any extent, it is always of advantage to have a 

 proper mallet and fet of wedges for tearing up wood and 

 other matters. 



WEDGWOOD, JosiAS, in Biography, was the younger 

 fon of a Staff^orddiire potter, and born in July 1730. His 

 education was reftrifted, but his mental powers were of a 

 fuperior kind, fo that by the fixed and perfevering exercife 

 of them he made very confiderable improvement in the art 

 of pottery to whicli his attention was direfted, and gave a 

 name as well as reputation to the place of his nativity. ( See 

 Pottery and The Potteries. ) His patrimony was fmall, 

 but by his fuper-emiiicnt ilvill and fteady apphcation he was 

 the founder of his own fortune as well as fame. The prin- 

 cipal feat of the potteries of Staffbrdftiire was Burflem ; 

 and there is reafon to believe that they have exifted in or 

 near this place for many centuries, and even, as fome fay, 

 fince the time of the Romans. But they had continued for 

 a long time in the fame rude ftate in which Plot found them 

 when he furveyed this county. The merit of introducing 

 into this country improvements in the art of pottery muS 

 be afcribed to two brothers of the name of Eders, who 

 came hither from Holland about the year 1700, and fettled 

 in the neighbourhood of the StalFordftiire potteries. They 

 manufaftured a red unglazed porcelain from a clay, which 

 they found in the eftate on which they fettled, called 

 " Bradwell ;" but this was only the brown ilone ware, in 

 the compofition of which no flint is ufed ; but they made 

 ufe of fait in glazing it : this fait, or muriate of foda, was 

 thrown into the oven at a certain flage of the firing procefs, 

 and the pieces of ware were fo difpofed as to receive the 

 tumes of it on every part of their furfaces. The fumes, 

 however, occafioned an alarm in the neighbourhood, which 

 obliged them to leave the country. A fimilar manufaftory, 

 however, was foon after eftabUfhed at Shelton, in the Pot- 

 teries, by one of their workmen, whofe name was Aftbury, 

 and who had poftefled himfelf of their fecret ; and as it was 

 found very ufeful, it was tolerated by the inhabitants, though 

 on the day of glazing, the denfe offenfivc fumes from fifty 

 or fixty manufaftories filled the valleys, and covered the hills 

 through an extent of feveral miles. The white ftone ware, 

 G g and 



