lane; _d d'_ are the eccentric rods, and the link is
represented in its lowest position. The dotted lines _h' h''_ show the
position of the eccentric rods when the link is in its highest position,
and _l l'_ when in mid position.

206. _Q._--What is Cabrey's arrangement?

_A._--Mr. Cabrey makes his eccentric rod terminate in a pin which works
into a straight slotted lever, furnished with jaws similar to the jaws on
the eccentric rods of locomotives. By raising the pin of the eccentric rod
in this slot, the travel of the valve will be varied, and expansive action
will be the result.

207. _Q._--What other forms of apparatus are there for working steam
expansively?

_A._--They are too numerous for description here, but a few of them may be
enumerated. Fenton seeks to accomplish the desired object by introducing a
spiral feather on the crank axle, by moving the eccentric laterally against
which the eccentric is partially turned round so as to cut off the steam at
a different part of the stroke. Dodds seeks to attain the same end by
corresponding mechanical arrangements. Farcot, Edwards, and Lavagrian cut
off the steam by the application of a supplementary valve at the back of
the ordinary valve, which supplementary valve is moved by tappets fixed to
the valve casing. Bodmer, in 1841, and Meyer, in 1842, employed two slides
or blocks fitted over apertures in the ordinary slide valve, and which
blocks were approximated or set apart by a right and left handed screw
passing through both.[1] Hawthorn, in 1843, employed as an expansion valve
a species of frame lying on the ordinary cylinder face upon the outside of
the valve, and working up against the steam side of the valve at each end
so as to cut off the steam. In the same year Gonzenbach patented an
arrangement which consists of an additional slide valve and valve casing
placed on the back of the ordinary slide valve casing, and through this
supplementary valve the steam must first pass. This supplementary valve is
worked by a double ended lever, slotted at one end for the reception of a
pin on the valve link, the position of which in the slot determines the
throw of the supplementary valve, and the consequent degree of expansion.

208. _Q._--What is the arrangement of expansion valve used in the most
approved modern engines?

_A._--In modern engines, either marine or locomotive, it is found that if
they are fitted with the link motion, as they nearly all are, a very g