1564
THEORY AND PRACTICE OF ENGINEERING.
Book II.
meters are small, the arms at right angles may be sufficient; but in those of greater dia-meter, the arms will often require diagonal braces from one to the other, and these againstrutted to the outer rim; the more solid the framing, the more exact the movement;great attention is required to effect this,
In the construction of a chapelet it is necessary to consider the power that is to beemployed; it has been shown that at the building of the bridge of Orleans one put inmotion by twelve horses made 140 turns in an hour : the number of cogs upon thegreat wheel was 115, and of trundles upon the lantern 12: the height as well as width
SEE#
Fig. 2921
Fig. 2922.
allsti
of the buckets was 6 inches. As the chain passes over the staves of the lantern, it is raisedwith its load by the turning of the latter : the outer frame is generally made of wood thesides braced together at convenient distances, and trapped with iron.
The Archimedean screw is surrounded by a cylinder made generally of wood ; the spindle,round which the screw traverses, may either be made of the same material or of iron : thisancient and very useful power has already been described.
Fig. 2924.
Pumps are often made of timber, when there is a difficulty of obtaining those of metal :but the trough or pipe in which the plunger works can rarely be made sufficiently water-