ON RAISING AN» REMOVING WEIGHTS. 20i) 



sometimes inconvenient and detrimental: when, however, the man walks 

 upon the wheel, and not within it, this objection is in great measure obvi- 

 ated. A walking wheel requires to be provided with some method of pre- 

 venting the dangerous consequences of the rapid descent of the weight, in 

 case of an accidental fall of the labourer : for this purpose, a catch is usually 

 employed, to prevent any retrograde motion; a bar has also sometimes been 

 suspended from the axis of the wheel, on which tlic man may support him- 

 self with his hands, and other similar precautions have been adopted. Some- 

 times the plane of a walking wheel is but little inclined to tlie horizon, and 

 the man walks on its flat surface. In either case the labour of horses, asses, 

 or oxen, may be substituted for that of men : but for cranes this substitution 

 would be very disadvantageous, sinae nmch force would be lost in stopping 

 frequently so bulky a machine as would be required. The employment of a 

 turnspit dog is an humble example of the same operation, and even goats 

 appear to have been sometimes made to climb in a similar manner. In a 

 walking wheel used for raising water at Carisbrook Castle, in the Isle of 

 Wight, the work was performed by the same individual ass for the wliole of 

 forty five years preceding 1771. Walking wheels have also been invented, on 

 which horses were to act externally with their fore feet or hind feet only; 

 but they have seldom, if ever, been applied to practical purposes. In general 

 it is advisable that walking wheels for quadrupeds should present to them a 

 path as little elevated as possible; and it might probably be of advantage to 

 harness them either to a fixed point, or to a spring or weight, which would 

 enable them to exert a considerable force even in a horizontal direction; but 

 probably after all they might be more advantageo\isly employed in a circular 

 mill walk. (Plate XVII. Fig. 217.) 



Mr. White's crane affords a good specimen of an oblique walking wheel; 

 the force may be varied accordingly as the labourer stands at a point mcfie or 

 less distant from the centre; and in order to avoid accidents, a break is 

 always acting on the axis of the wheel by its friction, except when it is re- 

 moved by the pressure of the man's hand on a lever, upon which he leans as he 

 ■walks. The force is also varied in some cranes by changing the pinion, which 

 acts on the principal wheel, and an expanding drum has been contrived for 

 the same purpose, consisting of a number of bars moveable in spiral grooves, 



VOL. I. EC 



