The arched girders are connected together, in the central portion, by a system of diagonal bracing, as is shown on Figs. 2 and 7.  The carriage road on the platform consists of buckled plates resting on transverse girders spaced 6 ft. 6 in. apart, and covered with road metal, and for the sidewalks checkered plates are used.  The ironwork in the bridge weighs 400 tons, and cost 8,400 l.; the abutments cost 3,600_l._, making the total outlay on the structure 12,000_l_.  The bridge was tested by a uniformly distributed load of 82 lb. per sq. ft., and under this stress the arched girders deflected 1.06 in.  The horizontal and vertical oscillation of the bridge, which were carefully observed and graphically recorded by special instruments, were very slight.  The engineer of the work was Mr. G.B.  Biadego, of Genoa.—­Engineering.

* * * * *

PUMPING MACHINERY.

[Footnote:  A paper read at the Montreal Meeting of the British Association.]

By E.D.  LEAVITT, JR., Cambridgeport, Mass.

MINE PUMPING MACHINERY.

One of the earliest steam engines, of any size, introduced into America, was erected about the year 1763, at the Schuylkill copper mine, situated upon the Passaic River, in New Jersey.  All its principal parts were imported from England; and a Mr. Hornblower (the son, it is believed, of the well known engineer of that name) came to this country for the purpose of putting up and running this engine.

At the time when the manufacture of the engines for the Philadelphia Water Works was commenced, and as late as the year 1803, we find five engines, in addition to the one above mentioned, noticed as being used in this country:  two at the Philadelphia Water Works; one just about being started at the Manhattan Water Works, New York; one in Boston; and one in Roosevelt’s sawmill, New York; also a small one used by Oliver Evans to grind plaster of Paris, in Philadelphia.  Thus, at the period spoken of, out of seven steam engines known to be in America, four were pumping engines.

In the coal regions of Pennsylvania, a simple, high pressure, single acting Bull engine has been extensively adopted; the dimensions usually run from 36 inches to 80 inches in diameter, and a very common stroke is 10 feet.  At the Empire shaft, in the Schuylkill coal region, there is a very fine pair of these engines, with 80 inch cylinders, working 24 inch pumps.  The stroke of both steam pistons and pumps is 10 feet.  These Bull engines are placed either vertically or on an incline, as is most convenient for the workings.  The water valves are made either double, triple, or four beat, according as the pumps are large or small; and the beats are usually flat, and faced with leather.  Many flap-valves are also in use.  These are frequently arranged on conical seats, and work very well.