37'2 PHILOSOPHICAL TRANSACTIONS. [aNNO \72Q. 



shaft is turned here by bars or handspikes, such as bd, fd, or cd, the lower 

 part being strengthened with iron hoops above and below the holes at d, with 

 a pivot or iron axis turning in a hole in a piece, whose section is f. pp, are 

 two pins, which hold on a collar in which the upper part of the shaft turns. 

 CB, the shaft or axle of the gibbet, with pivots and iron hoops at top and 

 bottom, and a wheel of iron, y, having teeth perpendicular to its plane. This 

 wheel is led by a pinion, u, which is on the axis of the wheel x, by whose arms 

 a man standing at h may bring about the end of the gibbet g with the ram- 

 head r, and the weight hanging at it, either to the right or left, and easily 

 hold the gibbet in any position, ctpq, a strong piece or block, having three 

 pulleys, one vertical, and the other two horizontal, that the rope may run over 

 the first of them, and between the two others. 



Fig, 2 represents a horizontal section of the crane in its upper part, or 

 rather a view of it from the plane of the roof, supposing the roof taken off; 

 where the same letters mark the parts which have been described in fig. 1. 



Fig. 3 shows the inconveniencies in the motion of the gibbet, lbed re- 

 presents part of the wharf next the water, or precipice of a quarry, xpa 

 the block-piece which holds the three pulleys, expressed by the same letters 

 as in fig. 1 and 2. sgrc the arm of the gibbet, represented by vg, fig. i. 

 T the vertical pulley, p, q the horizontal pulleys, represented in another situa- 

 tion by p, q, when their centers from m, y, are brought to n and t. c is a 

 point directly over the pivot of the shaft, or axle of the gibbet, cl, c2, 

 c3, c4, c5, represent a line over the arm of the gibbet, or rather a plane 

 going through the middle of it, in several of its positions, when turned to- 

 wards the right hand, from its direct position cr. ct), c7, c8, cc, repre- 

 sent the several positions of the gibbet towards the left, the last pulley r, at 

 the end of the gibbet, immediately over the weight traversing in the circle 

 5, 4, 3, 2, ], 6, 7,8. 



When the gibbet is in the position eg, the rope runs directly over the middle 

 of its arm ; therefore the least force applied to r or r, can keep in its place the 

 greatest weight that can be drawn up by the crane, when suspended to the 

 ram-head. If the pulleys are at p and q, the gibbet loaded will also be without 

 labour retained in the position c2 on the right, and c6 on the left, and with 

 no great trouble in the position cl. 



But if the gibbet be brought over the wharf at 4 on the right, or at 8 on 

 the left, the rope will no longer run over the middle of the gibbet, but deviate 

 from it, so as to make with it the angle q4t, or o8n, and raise the weight 

 by the motion of the gibbet in proportion as the line q4, or o8, is longer than 

 t4, or n8 ; and therefore the weight will tend to run back towards g, in pro- 



