AMERICAN

RAILROAD JOURNAL.

491.

A Memoir on the Resistance: to Railway
'l‘rn.ins at Diircrcrnt Velocities.

Institution of Civil E'ngt'7icei's, Mary 26-
Sir John Rennie, president, in the chair.———
The paper read was “ A Memoir on the Re-
sistance to Railway Trains at Different Ve-
locities,” by Wyndham Harding, C. E. He
commenced his paper as follows:

In 1837, the speed attained on railways
was a recent subject of wonder. No sooner
was the fact of the daily attainment of speed
which then appeared extraordinary, estab-
lished, than the following questions presented
themselves and became of practical interest.
What were the resistances experienced at
these high velocities ‘I Were they solely
those due to friction and the gravity of the
train when ascending an inclination which
experiments showed to be independent of the
velocity of the moving mass, or were they
resistances which varied with the velocities,
and if so, from what cause did they arise, and
what ratio did they bear to the velocity? The
introduction ofa smooth iron rail and an iron
Wheel running upon it bid fair to reduce ma-
terially the surface resistance, which had,hi-
therto been the retarding force most felt in the
traction of wheel carriages. But it was clear
that a railway train, impelled as it was by the
action of a limited quantity of steam (a va-
por used at an elasticity only about four times
that of air,) would still have to encounter a
formidable resistance from the atmosphere,
as this resistance makes itself seriously felt
in the motions of all bodies, light or heavy,
passing through it, and increases rapidly with
the velocity. The existence of this retarding
cause was of course not overlooked b the
engineers engaged in the working of rail-
ways, and the development of the new system
of locomotion, but they had something else
to do at that time, than to sit down and write
on that or any other subject. So far as has
come to my knowledge, Mr. I-Ierapath in the
Railway Magazine of 1836, was the first
writer who drew attention to the practical ef-
fect which the rcsistance of the atmosphere
would have- upon railway trains moving at
high velocities, giving a table founded, not
on experiments, but, to use his own words
on deductions from physical principles, an
showing a computed arithmetical value of
the retarding force, in pounds, at various ve-
locities. N 0 recent experiments were at that
time extant on the resistance offered by the
air to bodies moving through it, and the ex-
periments recorded by Dr. Hutton and Smea-
ton, were, I believe it may be said, not satis-
factory, especially at high velocities. It was
therefore a matter of much importance and
interest to measure and determine the value
of the resistances, whether from the air or
other causes, which exhibit themselves in
railway trains moving at various velocities.‘

I. At the meeting of the British associa-
tion for the advancement of science, held at
Liverpool, in 1837, the subject was according-
ly discussed, when much discordance of opi-
nion was found to prevail with regard to it
among the members of the Mechanical sec-
tion, which included several railway engi-
neers. A committee was therefore appointed
to investigate the subject, consisting of Mr.

Rennie, Mr. (now Sir John) Macneil, Mr.
Locke, Dr. Lardner, Mr. Harman Earle and
Mr E. Woods; and under their superinten-
dence an elaborate experimental inquiry was
commenced, and continued during 1838 and
1839. In the autumn of 1838 it fortunately
happened that the question of resistance of
trains became the subject of discussion be-
tween Mr. Nicholas Woorl and Mr. Brunei,
on the occasion of the deliberation of the pro.
prietors of the Great Western railway as to
the expediency of altering the gauge of 7
feet to that of4 feet 8% inches, Mr. Nicholas
Wood adopting a much higher estimate of
the increase of resistance with the velocity
than Mr. Biuncl would admit. Mr. Brunel
maintained that the result arrived at by the
experiments of the committee of the British
association and Mr. N. Wood were altogether
fallacious, adducing arguments to invalidate
the conclusions to which they pointed, based-
on the modes of conducting the experiments,
and describing the arrangement by which he
intended to diminish whatever objectionable
amount of resistance (arising from the pas-
sage of the train through the air) might be
found to exist in practice, viz: by shaping
the front of the engine on a principle analo-
gous to that of the bow of a boat. The com-
mittce accordingly, in 1839, varied the modes
of making the experiments which had been
pursued in 1838, in order to check the first
experiments, and to ascertain how far any of
the objections raised to the mode of con-
ducting these experiments were of force. In
this series of experiments the measure of the
force of resistance was in each case obtained
by a comparison with the standard aflbrded
by the effect of the action of gravity on trains
of known weight passing over portions of
railway of known, inclinations. The results
of the experiments I propose to give in the
present paper, and shall refer for the details
to the printed reports and tables in the reports
of the British association.

II. In 1843, Mr. Scott Russell undertook
some experiments on the Sheffield and Man-
chester railway, with a view of ascertaining,
himselfi the resistances to trains at various
velocities. Mr. Scott Russell communicated
the result of these experiments to the British
association in 1844 ;_ but as the details were
not printed, I have given those of the experi-
ments on which I argue, as well as the gene-
ral results: Mr. Russell having afforded me
such details.

III. In 1844 and 1845 a new and very
satisfactory instrument, for measuring the re-
sistance of trains, was afforded in the atmos-
pheric apparatus erected on the Kingstown
and Dalkey line. The resistances of trains
indicated by that apparatus are referred to in

Mr. Robert Stephenson’s printed report on the '

atmospheric system; this particular branch
of the subject was also especially brought
under the attention of the members of this
institution by Mr. Bidder in 1845, who con-
tributed a table of resistances compiled from
the experiments detailed in Mr. R. Stephen-
son’s report.

IV. In May, 1845, the writer of these re-

clined plane of the Bristol and Gloucester
railway (1 in '74) with a view to ascertain
the resistances of trains in descending that
incline freely. The details and results of
these experiments will be given in the follow-
ing remarks. These are, so far as the writer
is aware, the only experiments of the sort on
record as to the resistances on trains running.
on a railway of 7 feet gauge——all the other
experiments named having been made on
railways of the 4 feet 8,} gauge.

V. In the commencement of the present
year, 1845, the writer made some experi-
ments on the Croydon atmospheric railway ;.
the details of those experiments, which are
treated of in the following remarks, will be
given.

VI. At the end ofthe year 1845, the gauge
commissioners ordered experiments to be made
on railways of either gauge. In these expe-
riments all the circumstances were carefully
noted ; they, therefore, afford the means of
comparing the effect due to the water evapo-
rated, under the known conditions, with the
work actually performed, in drawing trains
at various velocities from 20 to..60 miles per
hour.

VII. Mr. Scott Russell, in the commence-
ment of this ycar,3rriade experiments on trains
of the Southeastern railway with lVlorins'
dynamomctcr. This beautiful instrument,
which Mr. Russell lately exhibited to the in-
stitution,proniiscd to supply the want, so long
experienced by railway engineers, of a dyna-
mometcr whose indications can be trusted to.
The details and results of these experiments
will be given in the following remarks.

The measure of. the resistances in the se-
ries of experiments I., II., IV., V., is the ef-
fect of gravity on descending plains of known
inclinations. In the series III. and V., the
measure is the pressure on the travelling pis.
ton of the atmospheric apparatus indicated
by the travelling barometer, less an allow-
ance for the friction contingent on the travel-
ling piston and accessories. In the series
VII., the measure is the self-registered indi-
cation of the dynamometer.

In the series V1,, the measure is the effect
due to the quantity of water converted into
steam at a certain known pressure, acting in
a locomotive engine, of which the dimensions
are known. We have thus recently been put
in possession of two dynamometers, which
promise to be trustworthy, whereby to mea-
sure the resistance to railway trains at diffe-
rent velocities, namely, the difference of pres-
sure on either side of the travelling piston on
the atmospheric apparatus and Morins’ dyna-
mometer. We are, now in a position to com-
pare the resistances, measured by four diffe-
rent means.

The object of this paper is, out of this
large collection of experiments, to present in
the simplest form those results which afford
the means of measuring the resistances of
passenger trains, of different weights, running
at different velocities, on a railway in good
repair, with no fortuitous circumstances tend-
ing to increase the resistance, as it is thus
only that we may hope to obtain a series of

marks made a few experiments on the in-

facts which may enable us to determine prac-