glO tECTUR£ XVIII. 



SO as to form a greater or smaller cylinder at pleasure. In order to place the 

 weight in any situation that may be required, the pulley may be made to slide 

 horizontally on the gib or arm. (Plate XVII. Fig. 218.) 



A model of a crane was exhibited some years ago to the Royal Society, in 

 which a large wheel fixed to a short axis was made to roll round on a plane, 

 while the lower end of its axis was connected by a joint with another axis in 

 a vertical position: then the wheel, having to describe a circumference some- 

 what larger than its own, was turned slowly, and therefore powerfully, round 

 its axis, and the motion was communicated to the fixed axis. The machine, 

 however, appears to be more curious than useful. 



• 



Sometimes a steelyard has been combined with a crane, for weighing goods 

 at the same time that they are raised by it. A small crane, fixed in a carriage, 

 is convenient for loading and unloading goods. In France, the carts used on 

 the wharfs are generally so long as to reach the ground behind when depressed, 

 and to furnish an inclined plane, along which the goods are raised by a lever 

 and axis, or a kind of capstan, fixed in front. 



For taking hold of stones which are to be raised by means of a rope, a hole 

 is sometimes formed in them, wider within than at its opening, and in this 

 a lewis is inserted, consisting of two inverted wedges, separated by a plug, to 

 which they are fastened by a pin. (Plate XVII. Fig. 219.) 



When a rope or chain, which is to raise a weight, is so long as to require a 

 counterpoise, the effect of this may be varied according to the length of the 

 rope, which is unbent, by hanging it on a second rope or chain, which acts on 

 a spiral fusee, slowly turned by a wheel and pinion. 



The use of cranes is so extensive and so indispensable, that their forms 

 have been often multiplied on account of local circumstances, or even from 

 caprice; but the constructions which have been described appear to be of the 

 most general utility, and from them it will be easy to judge of others. 



When weights of any kind are simply to be removed from one situation to 



