Mr. Gurney, in perfecting this invention, has followed Dr. Franklin's
advice--to tire and begin again. It is now four years since he first
commenced his ingenious enterprise; and nearly two years since we
reported and illustrated the progress he had made. (_See_ MIRROR, vol.
x. page 393, or No. 287.) He began with a large boiler, but public
prejudice was too strong for it; and knowing people talked of high
pressure accidents; the steam, could not, of course, be altogether got
rid of, so to divide the danger, Mr. Gurney made his boiler in forty
welded iron pipes; still the steam ran in a main pipe beneath the
whole of the carriage, and the evil was but modified. At length the
inventer has detached the engine and boiler, or locomotive part of
the apparatus, which is now to be fastened to the carriage, and may
be considered as a STEAM-HORSE, with no more danger than we should
apprehend from a restive animal, in whose veins the steam or mettle
circulates with too high a pressure. Fair trials have been made of
the Improved Carriage on our common roads, the Premier has decided the
machine "to be of great national importance," from sundry experiments
witnessed by his grace, at Hounslow Barracks; and the coach is
announced "really to start next month (the 1st) in working--not
experimental journeys--for travellers between London and Bath."[1]
Crack upon crack will follow joke upon joke; the _Omnibus_, with its
phaeton-like coursers will be eclipsed; and a journey to Bath and the
Hot Wells by steam will soon be an everyday event.
Descriptions of Mr. Gurney's carriage have been so often before the
public, that extended detail is unnecessary. Besides, all our liege
subscribers will turn to the account in our No. 287. The recent
improvements have been perspicuously stated by Mr. Herapath, of
Cranford, in a letter in the _Times_ newspaper, and we cannot do
better than adopt and abridge a portion of his communication.
"The present differs from the earlier carriage, in several
improvements in the machinery, suggested by experiment; also in
having no propellers;[2] and in having only four wheels instead of
six; the apparatus for guiding being applied immediately to the two
fore-wheels, bearing a part of the weight, instead of two extra
leading wheels bearing little or none. No person can conceive the
absolute control this apparatus gives to the director of the carriage,
unless he has had the same opportunities of observing it which I
had in a ride with Mr. Gurney. Whilst the wheels obey the slightest
motions of the hand, a trifling pressure of the foot keeps them
inflexibly steady, however rough the ground. To the hind axle, which
is very strong, and bent into two cranks of nine inches radius, at
right angles to each other, is applied the propelling power by means
of pistons from two horizontal cylinders. By this contrivance, and a
peculiar mode of admitting the steam to the cylinders, Mr. Gurney has
very ingeniously avoided that cumbersome appendage to steam-engines,
the fly-wheel, and preserves uniformity of action by constantly having
one cylinder on full pressure, whilst the other is on the reduced
expansive. The dead points--that is, those in which a piston has no
effect from being in the same right line with its crank,--are also
cleared by the same means. For as the cranks are at right angles, when
one piston is at a dead point, the other has a position of maximum
effect, and is then urged by full steam power; but no sooner has the
former passed the dead point, than an expansion valve opens on it with
full steam, and closes on the latter. Firmly fixed to the extremities
of the axle, and at right angles to it, are the two 'carriers'--(two
strong irons extending each way to the felloes of the wheels.) These
irons may be bolted to the felloes of the wheels or not, or to the
felloes of one wheel only. Thus the power applied to the axle is
carried at once to the parts of the wheels of least stress--the
circumferences. By this artifice the wheels are required to be of no
greater strength and weight than ordinary carriage-wheels; and, like
them, they turn freely and independently on the axle; but one or
both may be secured as part and parcel of the axle, as circumstances
require. The carriage is consequently propelled by the friction or
hold which either or both hind-wheels, according as the power is
applied to them jointly or separately, have on the ground. Beneath
the hind part drop two irons, with flat feet, called 'shoe-drags.' A
well-contrived apparatus, with a spindle passing up through a hollow
cylinder, to which the guiding handle is affixed, enables the director
to force one or both drags tight on the road, so as to retard the
progress in a descent, or if he please, to raise the wheels off
the ground. The propulsive power of the wheels being by this means
destroyed, the carriage is arrested in a yard or two, though going at
the rate of eighteen or twenty miles an hour. On the right hand of the
director lies the handle of the throttle-valve, by which he has the
power of increasing or diminishing the supply of steam _ad libitum_,
and hence of retarding or accelerating the carriage's velocity. The
whole carriage and machinery weigh about 16 cwt., and with the full
complement of water and coke 20 or 22 cwt., of which, I am informed,
about 16 cwt. lie on the hind-wheels."
Mr. H. then enumerates the principle of the improvements:--"That
troublesome appendage the fly-wheel, as I have observed, Mr. Gurney
has rendered unnecessary. The danger to be apprehended in going over
rough pitching, from too rapid a generation of steam, he avoids by a
curious application of springs; and should these be insufficient, one
or two safety valves afford the _ultimatum_ of security. He ensures
an easy descent down the steepest declivity by his 'shoe-drags,' and
the power of reversing the action of the engines. His hands direct,
and his foot literally pinches obedience to the course over the
roughest and most refractory ground. The dreadful consequences of
boiler-bursting are annihilated by a judicious application of tubular
boilers. Should, indeed, a tube burst, a hiss about equal to that of a
hot nail plunged into water, contains the sum total of alarm, while a
few strokes with a hammer will set all to rights again. Lastly, he has
so contrived his 'carriers,' that they shall act without confining the
wheels, by which means there is none of that sliding and consequent
cutting up of the road, which, in sharp turnings, would result from
inflexible constraint.
"Hills and loose, slippery ground are well known to be the _res
adversæ_ of steam-carriages; on ordinary level roads they roll
along with rapid facility. In every ascent there are two additional
circumstances inimical to progressive motion. One is, that carriages
press less on the ground of a hill than on that of a plain, thus
giving the wheels a less forcible grasp or bite. But this may be
easily remedied in the structure of a carriage, and is not of very
material consequence in the steepest hills that we have. The other is
more serious. When a carriage ascends a hill, the weight or gravity of
the whole is decomposable into two--one perpendicular, and the other
parallel to the road. The former constitutes the pressure on the road,
the latter the additional work the engine has to perform. Universally
this is the same part of the whole carriage and its load together,
which the perpendicular ascent of the hill is of its length. With
these principles, if we knew the bite of the wheels on the road,
we could at once subject the powers of Mr. Gurney's carriage to
calculation.
"Now, from one of the experiments made in the barrack-yard, at
Hounslow, I find we can approximate towards it. For instance, with one
wheel only fixed to the 'carriers,' the carriage drew itself and load
of water and coke (about 1 ton), with three men on it, and a wagon
behind of 16 cwt. containing 27 soldiers. This, at the rate of 1-1/2
cwt. to a man, in round numbers is 4 tons. Estimating the force of
traction of spring carriages at a twelfth of the total weight, it
consequently gives a hold or bite on the road of 1-12 of 4 tons, or
6 2-3rds cwt. per wheel, or 13 1-3rd cwt. for the two wheels. This is
likewise the propelling force of the carriage. Supposing, therefore,
we were ascending a hill of 1 foot rise in 8, which I am assured
exceeds in steepness any hill we have, we should be able to draw a
load behind of 2 tons 2 cwt., or between 3 and 4 tons altogether....
"On a good level road I think it not improbable it might draw, instead
of 7 tons which our experiment would give, from 10 to 11, besides
its own weight, or 100 ordinary men, exclusive of 2 or 3 tons for
carriages; and up one of our steepest hills, 3 tons besides itself, or
25 men besides a ton for a carriage. This it would do at a rate of 8,
9, or 10 miles an hour. For it is a singular feature in this carriage,
and which was remarked by many at the time, that it maintained very
nearly the same speed with a wagon and 27 men, that it did with the
carriage and only 5 or 6 persons. But there is a fact connected with
this machine still more extraordinary. For instance, every additional
cwt. we shift on the hind or working wheels, will increase the power
of traction in our steepest hills upwards of 4 cwt., and on the
level road half a ton. Such, then, is the paradoxical nature of
steam-carriages, that the very circumstance which in animal exertion
would weaken and retard, will here multiply their strength and
accelerate. This, no doubt, Mr. Gurney's ingenuity will soon turn to
profitable account.
"It has often been asserted that carriages of this sort could not
go above 6 or 7 miles an hour. I can see no reasonable objection
to 20. The following fact, decided before a large company in the
barrack-yard, will best speak for itself:--At eighteen minutes after
three I ascended the carriage with Mr. Gurney. After we had gone about
half way round, 'Now,' said Mr. Gurney, 'I will show you her speed.'
He did, and we completed seven turns round the outside of the road
by twenty-eight minutes after three. If, therefore, as I was there
assured, two and a half turns measured one mile, we went 2.8 miles
in ten minutes; that is, at the rate of 16.8, or nearly 17 miles per
hour. But as Mr. Gurney slackened its motion once or twice in the
course of trial, to speak to some one, and did not go at an equal rate
all the way round for fear of accident in the crowd, it is clear that
sometimes we must have proceeded at the rate of upwards of twenty
miles an hour."
The Engraving will furnish the reader with a correct idea of such of
Mr. Gurney's improvements as are most interesting to the public. The
present arrangement is certainly very preferable to placing the boiler
and engine in immediate contact with the carriage, which is to convey
goods and passengers. Men of science are still much divided on the
practical economy of using steam instead of horses as a travelling
agent; but we hope, like all great contemporaries they may whet and
cultivate each other till the desired object is attained. One of them,
a writer in the _Atlas_, observes, that "if ultimately found capable
of being brought into public use, it would probably be most convenient
and desirable that several locomotive engines should be employed on
one line of road, in order that they might be exchanged at certain
stages for the purposes of examination, tightening of screws, and
other adjustments, which the jolting on passing over the road might
render necessary, and for the supply of fuel and water."
An effectively-coloured lithographic of Mr. Gurney's carriage (by
Shoesmith) has recently appeared at the printsellers', which we take
this opportunity of recommending to the notice of collectors and
scrappers.
[Footnote 1: "Literary Gazette," Sept. 19, 1829.]
[Footnote 2: The propellers, I am informed, are not absolutely
discarded. They are now not fixed, but movable, and reserved for
extreme possible emergencies, or for certain military purposes.]
* * * * *