Page:The Kinematics of Machinery.djvu/237

 BELT TRAINS. 215

can be proved to have been used by the Egyptians at least some 1500 years B.C.* Late discoveries, indeed, have made it appear ex- tremely probable that the nations which peopled America before the epoch of its present Indian inhabitants, were acquainted with it and used it.f The bow disappears very slowly from the lathes of our own clock and instrument makers, making way for an end- less cord mechanism of the kind shown in Pig. 142. From all this

FIG. 166.

we can form some idea of the difficulties which have surrounded the transition from the alternate to the continuous rotary motion produced by a cord or band.

How soon this latter came into use we cannot say with certainty Its extended use among almost all Asiatic nations, as a means of

FIG. 167.

driving a spindle, bespeaks a great antiquity for it. The crossed belt, Fig. 166, appears to be the older, and this again was preceded by an arrangement in which the belt or cord, crossed or open, was wound more than once round both pulleys, Fig. 167, in order to prevent slipping. 86 With this last arrangement a very imper- fect and incompletely constructed frame sufficed to make trans- mission of motion possible> for of course the friction of the cord

i p. 56.
 * Weiss, Kostilmkivnde i. (1860) p. 96. Wilkinson, Ancient Egyptians (1871)

t Ban. Drilling stone without metal, Smithsonian Report 1868, p. 898 ; where the existence in the stone age of stone and bone drums for drill-spindles is pointed out.