The spoon, as
shown, is at its lowest position. It will make a forward stroke, through
about one-sixth of a revolution, and will thus become filled with
mud and be lifted above the surface of the water. The motion will be
imparted to it by the chain and pulleys seen at outer end of the derrick
jib. The jib will then be swung round over the bank on a hopper barge
and its contents delivered. The requisite power is supplied by the steam
engine at the end of the pontoon. Messrs. Rennie have made several of
these little dredgers, which are found very useful and handy in shallow
water.--_The Engineer_.
[Illustration: SINGLE BUCKET DIPPER DREDGER.]
* * * * *
RAILWAY ALARM WHISTLE.
In order to prevent a train passing a danger signal during a fog or
snowstorm without being seen by the engineer, the Southern Railway
Company of France have attached to the locomotive a steam whistle, which
is controlled by the signal. The whistle is connected with an insulated
metallic brush placed under the engine. Between the rails there is a
projecting contact bar, faced with copper, which is swept by the brush
when the train passes. This contact piece is connected with the
positive pole of a voltaic battery, the negative pole of which is in
communication with a commutator on the signal post, from which a wire
leads to the ground.
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