JIBS ON A NEW CONSTRUCTION. 99 



reddi(h coloured nitrous acid gas, I was furprized by the 

 burfting forth of flame from the paper, which was confumed 

 by it in lefs than a minute, without cracking, as I expeded, 

 the receiver. I think it unneceflary to make any comments, 

 or give the rationalt of this fadl. 



Always your's faithfully, 



AMICUS. 



XIII. 



DejcriptionofaJibonanevjConJlrudion; hy Mr.]. Bramah, 

 Engineer, Communicated by the Inventor. 



J 



IBS of the ufual conftrudion turn on two folid gudgeons. Defcrlptlon of « 



jib on a new 

 eonftru^oR. 



The rope by which the goods are raifed, pafles over the J'** °" ^ "*'* 



upper gudgeon, and is confined between two fmall vertical 

 rollers, in order that it may conftantly lead fair with the pulley 

 or fheave at the extremity of the jib. According to this con* 

 flrudion, whenever the crane turns round its axis, the rope is 

 bended fo as to form an angle more or lefs acute, which caufesi 

 a great increafe of fri£lion, and produces a continual effort 

 to bring the arm of the jib into a parallel pofition to the inner 

 part of the rope. Thefe inconveniences may appear to be 

 trifling on paper, but in adual praflice they are of no fmall 

 importance, for they neceflarily imply a much greater exertion 

 of power in raifing goods, and the application of a conftant 

 force to keep the jib in the pofition that may be requifite ; 

 while the partial ftrefs which is exerted on only a few ftrands 

 of the rope, when bended into an acute angle, infallibly 

 deftroys it in a very (hort time. 



The fimple confi:rudion exhibited in Plate V. obviates all 

 thefe defeds, and at the fame time poflfefles the very defirable 

 property of permitting the jib ©f what is termed a campfliut or 

 landing crane, wholly to revolve round its axis, and to land 

 goods at any point of the circle defcribed by the arm of the 



It confifts in perforating the axis or pillar of the crane> and 

 in conducing the rope through this perforation by means o£ 

 an additional puUy fixed on the top of the arm of the jib. 



H2 Th« 



