BENDING WOOD. 31 



dntnefs and elafticity enable them to acquire any form that may 

 be defired ; fo that there are few to which the moll whimfical 

 figures may not be given, with due care and the requifite pre- 

 cautions ; but at the fame time we injure their natural confti- but injurious 

 tution, retard their progrefs, and frequently reduce them to a t0 l e timbcr « 

 ftate of conftraint and difeafe prejudicial to their growth. 



II. Of the bending of Dead Wood, 

 The bending of wood that is cut down and dead, though The bending of 



° • ° dead wood is 



more difficult, is yet more m ufe, becaufe we may choole fuch mo ft advantage- 

 as is beft adapted to the purpofe for which it is defigned, and ous# 

 then give it the fuitable curvature. 



The procefs generally employed is founded on the property The principle is 

 caloric poflTefies of augmenting the elafticity of wood by pene- he ^, a ^Ich in- 

 trating it, and diminiming this elafticity on quitting it. creafes the pli- 



Thuswhen we with to bend thin pieces, as the ftaves of ^ nefs of tim ' 

 barrels, or the planks of boats, we heat them at the part that 

 is to be curved, and bend them gradually as they grow hot. 



But heat applied to one part of the wood, while the other Pa «*»1 heat af- 

 is in contact with the air, heats it unequally, and increafes the unequal j and 

 pliablenefs but partially ; fo that on bending it, fome parts are occafions it to 

 ftiff and others yield, occafioning an unequal curvature, and crac or * Mner * 

 fometimes cracks or fplinters in the infide or on the furface of 

 the wood. The only method of remedying this inequality is 

 to heat the wood equally throughout. 



Furnaces or ftoves gradually heated are adapted to the pur- Furnaces or 

 pofeof affording a uniform heat, and confequently facilitating ftj vesheatit 

 the curvature of the wood; but in ufing them there is reafon ma y fcorch it. 

 to fear, that the caloric, while heating the wood, may expel 

 from it the fluids contained in it, char it, and wholly deftroy 

 its elafticity. 



The pliablenefs of wood is in proportion not to its temper- Humidity as 

 ature alone, but to its humidity likewife. The fame wood at ce ff ary tQ e re nder 

 the fame temperature will be more or lefs pliable in proportion wood pliable. 

 to the water contained in it; and at an equal degree of moif- 

 ture its elafticity will be proportional to its temperature. 



We have an inftance of the double influence of heat and The lingular 

 moifture in joining two pieces of wood with a tenon and mor- mortife^nd * 

 tife, where the mbrtife is only a third of the breadth of the tenon, 

 piece that is driven into it to form the joint. Thefe joints, fo 

 extraordinary in appearance, furprife people fo much, that 

 3 moft 



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