ater
friction, added to irregular motion, would probably neutralize the
saving, while if the engine were one in which initial condensation
assumed more usual proportions, the gain would be probably on the side
of variable pressure. Even as it was, the diagrams showed that the
missing quantity became enormously large as the expansion increased.
Judging only by the feed water accounted for by the indicator, the
automatic engine appeared greatly the more economical, but actual
measurement of the feed water disproved this. The position of the
automatic engine was, however, relatively more favorable when simple
than when compound.

In conclusion, the author referred to a trial with a condensing
engine, at 170 lb. absolute pressure, in which the feed water used was
15.1 lb., a result evidently capable of further improvement, and to an
efficiency trial of a combined central valve engine and Siemens'
dynamo, made for the Admiralty, at various powers. At the highest
power the ratio of external electrical horse power to indicated horse
power in the engine was 82.3 per cent. Taking the thermo-dynamic
efficiency of the engine at 80 per cent., that of the combined
apparatus would be nearly 66 per cent.

* * * * *

RAILWAY BRIDGE AT LACHINE.

The subject of our large illustration this week is a large steel
bridge carrying the Central Pacific Railway over the St. Lawrence
River at Lachine, near Montreal. The main features of this really
magnificent structure are the two great channel spans, each 408 feet
long. It will be noticed that the design combines, in a very ingenious
manner, an upper and a lower deck structure, the railway track being
laid on the top of the girders forming the side spans, and on the
lower flanges of the channel spans, which are crossed by continuous
girders, 75 feet deep, over the central pier, and supported by
brackets as shown. The upper of our two engravings shows the method of
constructing the principal spans, which were built outward from the
side piers, while the work on the center pier was extended on each
side to meet. It was built at the works of the Dominion Bridge
Company, Montreal, from the design of Mr. C. Shaler Smith, the
well-known American bridge engineer.--_Engineering._

[Illustration]

* * * * *

IMPROVED SCREW PROPELLER.

While the last few years have seen great advances made in the designs
of steamshi