LECTURE XX.

CONTENTS. - Diagonal Direct-Acting Engines, with Joy's Valve Gear and
Alley's Flexible Coupling, &c. - Paddle-Wheels - Radial Paddle-
Wheel - Feathering Paddle-wheels.

Diagonal Direct-Acting Engines. - This form of engine is very
convenient, and is now the most popular for fast paddle-wheel
river steamers of light draught. As will be seen from the
illustrations which we give, it is neither more nor less than a
horizontal engine set at such an angle, that the forward end is
elevated to suit the necessary height of the paddle shaft, while
the after end rests firmly on the ship's floor frames. It no doubt
takes up a larger fore and aft space than the oscillating type, but,
on the other hand, it occupies less space athwart-ship, and when
the framing is carefully designed, using wrought-iron and steel
wherever possible (instead of the older style of cast-iron framing),
the weight per horse-power does not in all probability exceed
that of its chief rival the oscillating engine. The weight is also
better distributed along the keel of the ship, and the stresses set
up by its action are chiefly in a fore and aft and downward
direction, and therefore easily resisted by the natural structure of
the vessel. Moreover, the chief working parts are in full view
of the engineer while at the starting wheel, the engine is readily
got at for adjustment and repairs, easily compounded, and all the
most modern and efficient devices for quickly starting, stopping.
and reversing, or for economising steam are easily applied to it.
We illustrate one of the latest of these popular diagonal direct-
acting engines, of which eight sets with their boilers, &c., were
made last year (1885) by Messrs. Alley & Maclellan, Sentinel
Works, Glasgow, for steamers now trading on some of the large
rivers in India.

By studying the two figures, along with the index of parts, the
student will be able to get a minute idea of the general arrange-
ment of boilers and engines, but, in order that he may the better
grasp the construction of the engines, we illustrate a perspective
view of them as they lay in the workshop before being removed
and fitted into the steamers. It will be observed that they are
compound condensing engines, and are fitted with all the latest