The Sun.
London, England, 1851-04-10 00:00:00

INSTITUTION OF CIVIL ENGINEERS.
P.,
.• .

,
0 ,y, taL, Da-eiiptiou
of two Bridges over the river Dun and the Canal, with
the Lodge and Approaches, on the estate of Sir Joseph
Copley, Bart., at Spotbro', near Doncaster," by Mr. H.
Carr, Assoc. Inst. C.E.

The object of these works was to form an always ac-
cessible means of communication between the village of
Spotbro', situated on the north bank of the river Don,
and the south side, the only means hitherto existing having
been by an ancient ferry, which, from being situated im-
mediately above a weir, was extremely dangerous in
times of flood, and often perfectly unavailable. The
works comprised a bridge of seven arches over the river
Don, and another bridge of one arch over a short navi-
gable cut, or canal, which had been made for the im-
provement of the river navigation; with the necessary
embanked roads and approaches, and a lodge and gates
at the junction with the old road on the Spotbro' side.
Tne total length of these works was nearly one-third of
a mile.

The river bridge consisted of a centre arch of 100 feet
span, and three land arches on each side of 20 feet span
each. The centre arch was composed of four laminated
timber ribs, the outside planks of which were scarfed, and
the interior ones set with a small space between the butt
ends, so as to allow the whole to be keyed up by driving
in hard eak wedges, when the arch was laid, and spikes
were used instead of treenails. On removing the
lagging of the centres, on which the ribs were framed, it
was found that the weight was taken by the sides of the
wedges, but even this .was thought not to be so objec-
tionable as the imperfetion in the butt joint in the ordi-
nary construction.
The interior of the land arches was constructed of
brick-work, set in cement; the rest of the work being
composed principally of pitch faced ashlar and rubble.
The bridge over the canal was fifty-four feet span,
and ten feet nine inches rise. It was constructed in a
similar manner and of like materials to the land arches
of the river bridge, and had Sir Joseph Copley's arms
carved in stone on two spandrils, and his initials reversed
and entwined on the other two.

The works were executed by Messrs. T. and J.
Waring, of Swinton, and occupied about fourteen months
in construction at a cost of about 7,6501.
The next paper read was "On the Nominal Horse
Power' of Steam Engines," by Commander L. G.
Heath, R.N.
The inadequacy of the present term " nominal horse
power" for giving a definite idea, either of the ab-
solute, or relative power of engines was first ex-
amined, by comparing the engines of her Ma-
jesty's steamer Garland and Basilisk, which were
both constructed on the same principle, with oscillating
cylynders, and were both used to drive paddle-wheels.
This comparison was made under three distinct beads
the mean effective pressure, the number of revolutions
per urinate, and the size of the cylinders. It was urgd
that Watt's constant of 71bs. per square inch, for the
mean effective pressure, was not only in itself inappli-
cable, but that no constant quantity could be universally
applicable. Also, that the me, hod of determining the
number of revolutions per minute, from a conventional
,peed, founded on the length of stroke of the piston, was
((pally fallacious.
It was, therefore, proposed that the term "nominal
horse power" should be abolished, and that engines should
in future be designated by the cubic contents of their
steam cylinders, jointly with their nominal consumption
of a standard description of fuel during a given period of
ono hour. A table might be drawn up giving this no-
minal consumption in terms of the grate and the heating
sui face, and should be accompanied by rules and direc-
tions for ensuring the uniform measurement of the grate
and the heating surface. This system, it was contended,
would be more in accordance with the present practice of
construction, and would enable the relative size and
power of engines to be more accurately estimated than
by the present method.
The discussion was adjourned until the meeting of
April 15th, when the following paper will be read:—" On
Foundations; natural and artificial," by Mr. S. Clegg,
jun., M. Inst. C. E.