£36 Improved Crane and Ft exilic Chains. 



portations. — The durability is at least six to one in favour of 

 chains. 



Though the model of the crane is chiefly intended to con- 

 vey a proper idea of the new method of working chains, yet 

 I trust it will be found to possess several other advantages in 

 point of construction, which are .entirely new, and calcu- 

 lated to increase the safety and durability, as well as to les- 

 Jen the expense of that useful machine. 



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

 gudgeons are the points of resistance to the machine and its 

 load, and consequently the effect of the transverse strain up- 

 on the perpendicular will be in proportion to 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 mor- 

 tise for the diagonal stay, from the lower one. 



Notwithstanding these circumstances are so evident, they 

 are seldom attended to ; for in general a large and expen- 

 sive piece of oak, sufficient of itself to make a crane of 

 double the purchase, forms .the perpendicular ; the gib is- 

 jjiortised into it, at eighteen or twenty inches from the top, 

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

 iive or six feet from the bottom, tg allow a birth below for 

 the barrel. Thus the effect of the transverse and oblique 

 strains of the gib and diagonal stay npon the perpendicular, 

 is increased by their distances from the gudgeons, or points 

 of resistance, and the perpendicular itself considerably 

 weakened by mortises made where the greatest strength is 

 required. • Hence the frequent failure of cranes of the com- 

 mon construction, bv the breaking pf the perpendiculars in 

 the mortises. 



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

 formed of wood, cannot be connected together in any other 

 way than by mortising ; and as this method considerably 

 diminishes the. strength of the timber, I make use of cast- 

 iron morl ise pieces. 



The perpendicular is formed of two oak planks, each 

 eighteen inches wide, four thick, and sixteen feet long ; 

 these, at the top and bottom, are let into cast-iron mortise 

 pieces, which retain the planks ten inches asunder. The 



barrel 



