ments upon
steel; but I speak of it as a matter of congratulation that, in lieu
of such machines being used by the few, and at rare intervals upon
small specimens, for experimental purposes, they are now employed in
daily practice and on a large scale.

In harbor work we have had the principle of construction employed by
Mr. Stoney at Dublin, where cement masonry is moulded into the form
of the wall for its whole height and thickness, and for such a length
forward as can be admitted, having regard to the practical limit of
the weight of the block, and then, the block being carried to its
place, is lowered on to the bottom, which has been prepared to receive
it, and is secured to the work already executed by groove and tongue.

It would not be right, even in this brief notice of such a mode
of construction, to omit mention of the very carefully thought out
apparatus by which the blocks are raised off the seats whereon they
have been made, and are transported to their destination. It is no
simple undertaking (even in these days) to raise (otherwise than
hydraulically) a weight of 350 tons, which is the weight of the
blocks with which Mr. Stoney deals. But he does this by means of
pulley-blocks attached to shears built on the vessel which is to
transport the block, and he contrives to lift the weight without
putting upon his chains the extra strain due to the friction of the
numerous pulleys over which they pass. The height of the lift is only
the few inches needed to raise the block clear of the quay on which it
has been formed, and this is obtained by winding up the chain by steam
gear quite taut, so as to take a considerable strain, but not that
equal to the weight of the block, and then water is pumped into the
opposite end of the vessel to that upon which the shears are carried,
this latter end rises, and the block is raised off the seat on which
it was formed, without the chains being put to work to do the actual
lifting at all. The vessel, with the block suspended to the shear legs
and over the bows, is then ready to be removed to the place where
the block has to be laid. A word must here be said about an extremely
ingenious mode of dealing with the slack chain, to prevent its
becoming fouled, and not paying out properly, when the block is being
lowered. This is accomplished by reeving the slack of each chain over
two fixed sets of multiple sheaves.

A donkey-engine works a little crab having a large drum, the ch