WALKING-WHEEL. A mechanical contrivance by means of which the dead weight of men, or animals, acting upon one side of a wheel by walking upwards, is made to act as the motive power of the machine to which it is applied. It is frequently used in quarrying operations, or in agricultural districts, where labour is cheap ; but in large towns it is rarely the case that the wheel-eranes can be advan tageously employed, because in those localities artificial sources of power, or the more complicated adaptations of machinery, are found to be more economical than the employment of the dead weight of human beings. The walking-wheels were, however, much used in engineering and architecture in the last century, and they are retained at the present day in the quarries around Paris; but the tendency of modern practice is unquestionably to lead to their abandonment in favour of more perfect mechanical contrivances.
The walking-wheel used by Peyrounet at the bridge of Orleans is a good illustration of this class of engines. It consisted of an upright post, or pivot, supported by a strong framework of timber, bearing, upon a metal pivot at its head, an inclined beam, projecting on one side to farm the arm of the pulley, and on the other to support the windlass and the walking-wheel. The weights upon either side of the pivot were arranged in such wise that they balanced one another as nearly as possible when the machine was in work ; and the motion was given by the movement of the men walking in the interior of the wheel. The power exercised, therefore, in these engines depends upon the ratio of the radius of the men's path to the radius of the axle, and upon the weight of the men employed; and as in quarrying operations it is possible to increase the diameter of the walking-wheels to almost any dimension which may be desired, they are usually made of great size. Peyronnet made his wheels about 12 feet 9 inches in diameter; near Paris they are sometimes made of from 16 feet to 18 feet in diameter. Generally speaking the men walk on the inside of the wheel : but occasionally they tread upon, and hold by, rounds placed upon the periphery of the wheel ; in either case it is essential to provide means by which the motion should be regulated and the men may be prevented from making false steps. If the load at the extremity of
the arm should at any time, for instance, exceed the weight of the counterbalancing machinery, there would be a danger of its over powering the men and of causing the wheel to run backwards ; the consequences of such an accident would be, in all probability, fatal to the men employed ; and it is therefore essential to bear in mind that the useful range of the use of walking-cranes must be limited to the narrow bounds of the weights on the respective aides of the machinery. Walking-wheels are seldom used, even in rude districts, when the weight to be raised exceeds four tons.
Animal power is occasionally applied to.walking-wheels by making horses, donkeys, and even dogs, move in them ; but all these animals exercise so much greater power when pulling against a cellar in a horizontal direction, that they are more commonly and more advan tageously employed In horizontal mills than in the vertical walking wheels. The old-fashioned turnspit wheels formerly in use In mediaeval kitchens afford familiar illustrations of this class of machinery.
The tread-wheels used for the punishment of offenders are, in fact, walking-wheels ; but in them the wheels are designedly so balanced that the mere weight of the prisoners placed upon the boards causes the wheels to revolve, and thus to bring in succession the various boards under the feet of the men, who are compelled to tread upon each of these boards, unless they prefer receiving very heavy and painful blows. No use is made of the power thus exerted, and it seems to be one of the most painful considerations connected with this mode of punishment, that the men feel and know that they are working in vain.
(Peyronnet, Nourel Architecture Hydrauligue ; Borgnis, Trait/ de 4116eanique.)