370 HHILOSUVHICAL TRANSACTIONS. [aNNO i.72Q. 



little above b, to turn it by; but in that case too the force is unequal, as the 

 weight is carried round; so that the lives of the men that are loading, often 

 depend on the care of the man who guides the weight, by either of the means 

 abovementioned. 



But if upon the axis of the gibbet there be fixed an iron wheel, y, with many 

 teeth, to be carried round by a pinion, u, of a few leaves, on the end of whose 

 axis is fastened a wheel, x, with arms (that axis going through the perpendicu- 

 lar piece Tz behind the shaft of the gibbet) a man standing at that wheel is 

 out of harm's way, and has such an advantage of power as to hold the weight 

 steady in any place required, notwithstanding its tendency to swing, which is 

 not felt at the ends of the arms of this last wheel. The first who has made 

 use of this contrivance is Mr. Ralph Allen, Post-master of Bath, at his Stone- 

 Quarry, where the weight raised is 4 or 5, and sometimes 6 or 7 tons. It 

 need not be remarked, that the power to bring up the weight works here by 

 means of a capstan, or upright shaft, r.o, drawn round by liorses, that the 

 weight may come up more expeditiously, though in the figure the hand- 

 spikes, f, e, b, going in at such a hole as d, show that men may work it 

 on occasion. 



The same gentleman has another crane at the river side, where he has a 

 wharf, by which he takes the stone from the carriages, and with great expedi- 

 tion lets it down into the barges or vessels that come to fetch it. 



This crane is of the sort commonly called a rat's tail crane, fig. 7? moving 

 round a strong post like a windmill, so that it may turn quite round with all 

 its load. The axle Bb, on which the rope winds, is here horizontal like a 

 winch ; but to gain strength, instead of the walking wheel ca, it is carried 

 round by a strong wheel and pinion, fig. 5 and 6; or is in efi^ect a double axis 

 in peritrochio. Now in the common cranes of this kind, there is only a 

 catch, as eka, fig. 5, to hold the burthen at the height it is brought up to, 

 while the crane is turned round, to have the weight lowered into the vessels, 

 which is done by lifting up the catch, and being ready to let it down again as 

 need requires. Sometimes a half circumference of wood, diib, fig. 5, is held 

 hard against a wooden wheel ww, on the axle, to regulate and govern the 

 descent of the weight. But as in either of these cases, if the man at the crane 

 is careless, very bad accidents happen, he has made such a contrivance, that the 

 pall or lever, by which the axle is pressed to direct the descending motion, so 

 communicates with the catch, that in case the man that ouglit to manage it, 

 shoi Id carelessly let it go, the catch always takes, and thus all accidents are 

 prevented; as will be shown in the explanation of fig. 5 and 6. 



