ArrLICATlON OF CIIAIXS. J 3 1 



oblique strains of the gib and diagonal stay upoti I he per- 

 pendicular, is increased by their distances from the 

 gudgeons, or points of resistanctj, and the perpendicular 

 itself considerably weakened by mortises made where the 

 greatest str(?ngth is rcqiiirud. Hence the frequent failure 

 of cranes of the common construction, by the breaking 

 of the perpendiculars in the mortises. 



It appears, however, that the various parts of a crane Improvement. 



formed of wood, cannot be connected together in any 9^^^"*.^°" ^^''- 



' _ , ^ >' tise pieces. 



other way than by mortising ; and as this metiiod consi- 

 derably diminishes the strength of the timber^ I make 

 use of cast-iron mortise pieces. 



The perpendicular is formed of two oak planks, each, ^^^hod of 

 eighteen inches' wide, four thick, and sixteen feet long; '^^"^"^S' 

 these, atthe top.and bottom, are let into cast-iron mortise 

 pieces, which retain the i>lanks ten inches asunder. The 

 barrel for the chain, works between them. The piece at 

 the top contains in the middle a dove-tailed mortise, into 

 which a stock for the gib is fixed; for greater security, 

 an iron bolt goes through the whole ; the stock projects 

 two feet from the mortise, and a plank eighteen inches 

 deep, and four thick, is bolted to each side of it to form 

 the gib, the interstice between the planks forming a birth 

 for the top block to slide in. The diagonal stay is of the 

 same dimensions, formed in a similar manner, and con- 

 nected to the perpendicular, by being let into the lower 

 mortise piece. 



In this mode of construction scarcely any part of the Advantages of 

 timber is cut away ; and the stretjgth of the materials, so [j^^^ dctaiH.cd^'^" 

 far from being diminished, is augmented by the cast-iron 

 mortise-pieces, the gib is brought much closer to the 

 upper gudgeon, and the centre lines of the perpendicular 

 and ihe diagonal stay, crossing each other at the top of 

 the lower one, places the whole strain as near as possible 

 in a line with the gudgeons. The business of the perpen- 

 dicular becomes in consequence little more than that of a 

 mere prop, and consequently requires no greater strength 

 of materials than the diagonal stay. "" 



The top block is made of cast-iron, and has a groove 

 three inches deep on each side, for the purpose of em- 

 bracing the planks which form the gib, 



S 2 Tq 



