130 APPLICATION OF CHAINS. 



The oblique The links of a chain are subject to the transverse straiiT, 

 strain from i xl • ^ , i ^ t . • • • 



bearing is in- "^^'"^''^ "^hey move hi contact ; but as such strain is in pro- 



considcrablc. portion to the length of the bearing, it min>t be very 

 trifling. AH the links having axles of their oivn, the 

 chain moves shnuKancously icUh /he stridn^ and both arc 

 in cunvcqncncc retained in cunliniial equilibria. A chain 

 in grooves will therefore sustain as great a weight when 

 bent over a pulley, as it will in a direct line, and conse* 

 quently is safer than a rope. 

 Chains are less ^ ^^^^' ^"^'^^''"b ^^^ flexible method of applying 

 affected by ex- chains ill the working of machinery, has long been a <le- 



posure than sidcratum in the arts : for they are but little affected by 



ropes. -^ v^ 



exposure to the weather, or the heat of manufactorieSj 



whilst either produces the speedy destruction of ropes. 

 — . and la^t This discovery is of additional importance, as it sub- 

 six times as stitutes a durable article for a very perishable one, and 

 ^* gives employment to our own manufactories at the cx- 



penceof foreign importations. — The durability is at least 

 six to one in favour of chains. 

 The author's Though the drawing of the crane is chiefly intended to 

 luable im- ^^' convey a proper idea of the new method of working 

 provcments. chains, y^t it will be found to possess several other ad- 

 vantages in, point of construction, wjiich are entirely new, 

 and calculated to increase tlie safety and durability, as 

 w^ell as to lessen the expence of that useful machine. 

 The mortises On reviewing the principles of a crane, we find that 



of the trans- ^jj^ gudgeons are the points of resistance to the machine 



verse pieces are '■,.?, , , , v, ^ i 



commonly dis- ^"" ^^^ load, and consequently the enect ot the transverse 



tant from the strain upon the perpendicular, will be in proportion to 



** S^°"®* the distance of the mortise, for the gib from the upper 



one ; and that of the oblique strain, in proportion to the 



distance of the mortise for the diagonal stay, from the 



lower one. 



-—which re- Notwithstanding these circumstances are so evident, 



quires a ^jj(.y g^e seldom attended to ; for in general a large and 



streninhoftipi- "^ , . ^ , ^. . ^. ,.. , 



ber in the up- expensive piece of oak, sumcient ot itselt to make a crane 



right piece. of double the purchase, forms the perpendicular ; the gib 

 'n mortised into it, at eighteen or twenty inches from the 

 top, to make room for the gudgeon, as is the diagonal stay 

 at live or six feet from the bottom, to allow a birth be- 

 low for the barrel. Thus the effect of the transverse and 

 J oblique 



