Chat-. XII.
100.5
sime scantling, 00 feet in length ; into the ends of this are framed two inclined braces,S9 feet in length and 7 inches square, secured by three iron bolts to the head of the in-clined timber, 39 feet in length, as shown to the left of the figure. The post of the crane,
WHARP CRANE.
12 inches square, works on a gudgeon, both at top and bottom ; the inclined piece holdinga metal box for the foremen, and the sill, that for the latter to work in. The gib, 12 feet inlength and 12 inches square, is braced by another piece, 6 inches by 4. This kind ofcrane with a wheel 3 feet 4 inches diameter, and pinion 6 inches, is much used inScotland .
Another variety of wharf crane is shown in the accompanying figure, where the framingis formed above, not lying immediately on the ground. The plan of the top is triangu'ar,each side being 29 feet in length, and 12 inches square, secured at the angles by cast-iron
Fig. 1515.
boxes, and cross-braced. The upright post, 12 inches square, works top and bottom on agudgeon, and the gib, 14 feet in length, and 12 inches square, is braced to it by a piece 6inches square. By this crane ordinary weights are landed at the wharfs of many of the canals.
"When the wheel and axle are applied to raisea weight, the velocity with which the pow’ermoves is as many times greater than that withwhich the weight rises, as the weight itself isgreater than the power; hence it is that in theelevation of the weight a quantity of power isexpended equal to that which is required toelevate the weight, if the power were imme-diately applied to it without using any machine.
V> hen in one revolution of the machine thelength of rope uncoiled from the wheel is equalto the circumference of the wheel, it is throughthat space the power must move ; and at thesame time we shall findthat the length of ropecoiled upon the axle isequal to the circumferenceof the axle, and throughthis space the weightmust be raised; thespaces, therefore, through
which the power and Fig. 1516. wharf crane.
weight move in the same time are in the proportion of the wheel and axle, and these
VT* yi5s
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