OF CRANES. 91 



As the ends of the sails nearest the axis cannot move LECT 

 with the same velocity that the tips or farthest ends do, ^^^^ 

 although the wind acts equally strong upon them ; per- 

 haps a better position than that of stretching them 

 along the arms directly from the center of motion, might 

 be to have them set perpendicularly across the farther 

 ends of the arms, and there adjusted lengthwise to the 

 proper angle. For, in that case, both ends of the sails 

 would move with the same velocity ; and being farther 

 from the center of motion, they would have so much 

 the more power : and then, there would be no occasion 

 for having them so large as they are generally made ; 

 which would render them lighter, and consequently, there 

 would be so much the less friction on the thick neck of 

 the axle where it turns in the wall. 



A crane is an engine by which great weights are A 

 raised to certain heights, or let down to certain depths. 

 It consists of wheels, axles, pulleys, ropes, and a gib or 

 gibbet. When the rope H (Plate II.) is hooked to the 

 weight K, a man turns the winch A, on the axis where- 

 of is the trundle B, which turns the wheel C, on whose 

 axis D is the trundle E, which turns the wheel F with 

 its upright axis G, on which the great rope H H winds 

 as the wheel turns : and going over a pulley / at the 

 end of the arm d of the gib cede, it draws up the 

 heavy burden K; which, being raised to a proper 

 height, as from a ship to the quay, is then brought over 

 the quay by pulling the wheel Z round by the handles 

 z, z, which turns the gib by means of the half wheel b 

 fixed on the gib-post c c, and the strong pinion a fixed on 

 the axis of the wheel Z. This wheel gives the man that 

 turns it an absolute command over the gib, so as to 

 prevent it from taking any unlucky swing, such as often 

 happens when it is only guided by a rope tied to its arm 

 d; and people are frequently hurt, sometimes killed, by 

 such accidents. 



