‹‹‹ Vitr. 10.3.8 | Table of Contents | Vitr. 10.4.1 ›››
9Now as small wheels revolve with more difficulty than larger ones, so levers and yokes press most on the side which is the least distance from the fulcrum, and on the contrary they ease those who bear that arm which is at the greatest distance from the fulcrum. Inasmuch as all these machines regulate either rectilinear or circular motion by means of the centre or fulcrum, so also waggons, chariots, drumwheels, wheels of carriages, screws, scorpions, balistæ, presses, and other instruments, for the same reasons produce their effects by means of rectilinear and circular motions.
9Just as smaller wheels move harder and with greater difficulty than larger ones, so, in the case of the poles and yokes, the parts where the interval from centre to end is less, bear down hard upon the neck, but where the distance from the same centre is greater, they ease the burden both for draught and carriage. As in all these cases motion is obtained by means of right lines at the centre and by circles, so also farm waggons, travelling carriages, drums, mills, screws, scorpiones, ballistae, pressbeams, and all other machines, produce the results intended, on the same principles, by turning about a rectilinear axis and by the revolution of a circle.