+--------------------+------------------+-----------+-------------+
| | Diameter of | Size of | |
| | driving wheels. | cylinder. | Position of |
| | ft. in. | in. in. | cylinder. |
+--------------------+------------------+-----------+-------------+
|Great Eastern | 7 0 | 18 × 24 | inside |
+--------------------+------------------+-----------+-------------+
|South-Eastern | 7 0 | 19 × 26 | " |
+--------------------+------------------+-----------+-------------+
|Glasgow and | | | |
|Southwestern | 6 1 | 18 × 26 | " |
+--------------------+------------------+-----------+-------------+
|Midland, 1884 | 7 0 | 19 × 26 | " |
+--------------------+------------------+-----------+-------------+
|North-Eastern | 7 0 | 17½ × 24 | " |
+--------------------+------------------+-----------+-------------+
|London and | | | |
|North-Western | 6 6 | 17 × 24 | " |
+--------------------+------------------+-----------+-------------+
|Lancashire and | | | |
|Yorkshire | 6 0 | 17½ × 26 | " |
+--------------------+------------------+-----------+-------------+
|North British | 6 4 | 17 × 24 | " |
+--------------------+------------------+-----------+-------------+
|Nord | 7 0 | 17 × 24 | " |
+--------------------+------------------+-----------+-------------+
|Paris-Orleans, 1884 | 6 8 | 17 × 23½ | outside. |
+--------------------+------------------+-----------+-------------+
|Ouest | 6 0 | 17¼ × 25½| " |
+-----------------------------------------------------------------+
This table, the examination of which will be found very instructive,
shows that there are already in use: For locomotives with single
drivers, diameters of 9 ft., 8 ft. 1 in., and 8 ft.; (2) for
locomotives with four coupled wheels, diameters 6 ft. to 7 ft. There
is therefore an important difference between the diameters of the
coupled wheels of 7 ft. and those of 8 ft. 3 in., as conceived by M.
Estrade. However, the transition is not illogically sudden, and if the
conception is a bold one, "it cannot," says M. Nansouty, "on the other
hand, be qualified as rash."
He goes on to consider, in the first place: Especial types of
uncoupled wheels, the diameters of which form useful samples for our
present case. The engines of the Bristol and Exeter line are express
tender engines, adopted on the English lines in 1853, some specimens
of which are still in use.[1] These engines have ten wheels, the
single drivers in the center, 9 ft. in diameter, and a four-wheeled
bogie at each end. The driving wheels have no flanges. The bogie
wheels are 4 ft. in diameter. The cylinders have a diameter of 16½ in.
and a piston stroke of 24 in. The boiler contains 180 tubes, and the
total weight of the engine is 42 tons. These locomotives, constructed
for 7 ft. gauge, have attained a speed of seventy-seven miles per
hour.
[Footnote 1: M. Nansouty is mistaken. None of the Bristol and
Exeter tank engines with. 9 ft. wheels are in use, so far as we
know. ED. E.]
The single driver locomotives of the Great Northern are powerful
engines in current use in England. The driving wheels carry 17 tons,
the heating surface is 1,160 square feet, the diameters of the
cylinders 18 in., and that of the driving wheels 8 ft. 1 in. We have
here, then, a diameter very near to that adopted by M. Estrade, and
which, together with the previous example, forms a precedent of great
interest. The locomotive of the Great Northern has a leading
four-wheeled bogie, which considerably increases the steadiness of the
engine, and counterbalances the disturbing effect of outside
cylinders. Acting on the same principles which have animated M.
Estrade, that is to say, with the aim of reducing the retarding
effects of rolling friction, the constructor of the locomotive of the
Great Northern has considerably increased the diameter of the wheels
of the bogie. In this engine all the bearing are inside, while the
cylinders are outside and horizontal. The tender has six wheels, also
of large dimensions. It is capable of containing three tons and a half
of coal and about 3,000 gallons of water. This type of engine is now
in current and daily use in England.
M. Nansouty next considers the broad gauge Great Western engines with
8 ft. driving wheels. The diameters of their wheels approach those of
M. Estrade, and exceed considerably in size any lately proposed. M.
Nansouty dwells especially upon the boiler power of the Great Western
railway, because one of the objections made to M. Estrade's locomotive
by the learned societies has been the difficulty of supplying boiler
power enough for high speeds contemplated; and he deals at
considerable length with a large number of English engines of maximum
power, the dimensions and performance of which are too well known to
our readers to need reproduction here.
Aware that a prominent weak point in M. Estrade's design is that, no
matter what size we make cylinders and wheels, we have ultimately to
depend on the boiler for power, M. Nansouty argues that M. Estrade
having provided more surface than is to be found in any other engine,
must be successful. But the total heating surface in the engine, which
we illustrate, is but 1,400 square feet, while that of the Great
Western engines, on which he lays such stress, is 2,300 square feet,
and the table which he gives of the heating surface of various English
engines really means very little. It is quite true that there are no
engines working in England with much over 1,500 square feet of
surface, except those on the broad gauge, but it does not follow that
because they manage to make an average of 53 miles an hour that an
addition of 500 square feet would enable them to run at a speed higher
by 20 miles an hour. There are engines in France, however, which have
as much as 1,600 square feet, as, for example, on the Paris-Orleans
line, but we have never heard that these engines attain a speed of 80
miles an hour.
Leaving the question of boiler power, M. Nansouty goes on to consider
the question of adhesion. About this he says:
Is the locomotive proposed by M. Estrade under abnormal conditions as
to weight and adhesion? This appears to have been doubted, especially
taking into consideration its height and elegant appearance. We shall
again reply here by figures, while remarking that the adhesion of
locomotives increases with the speed, according to laws still unknown
or imperfectly understood, and that consequently for extreme speeds,
ignorance of the value of the coefficiency of adhesion f in the
formula
d 2 I
fP = 0.65 p ------- - R
D
renders it impossible to pronounce upon it before the trials earnestly
and justly demanded by the author of this new system. In present
practice f = 1/7 is admitted. M. Nansouty gives in a table a
_resume_ of the experience on this subject, and goes on:
"The English engineers, as will be seen, make a single axle support
more than 17 tons. In France the maximum weight admitted is 14 tons,
and the constructor of the Estrade locomotive has kept a little below
this figure. The question of total weight appears to be secondary in a
great measure, for, taking the models with uncoupled wheels, the
English engines for great speed have on an average, for a smaller
total weight, an adhesion equal to that of the French locomotives. The
P.L.M. type of engine, which has eight wheels, four of which are
coupled, throws only 28.6 tons upon the latter, being 58 per cent. of
the total weight. On the other hand, that of the English Great Eastern
throws 68 per cent. of the total weight on the driving wheels.
Numerous other examples could be cited. We cannot, we repeat, give an
opinion rashly as to the calculation of adhesion for the high speed
Estrade locomotive before complete trials have taken place which will
enable us to judge of the particular coefficients for this entirely
new case."