Essay by Robert Stephenson on the construction of the Rocket locomotive
- part of archive:
- Correspondence from Robert Stephenson to Samuel Smiles
- Stephenson, Robert
An essay by Robert Stephenson regarding the construction and design of the Rocket locomotive. Essay was sent to Samuel Smiles to aid in the writing of his biography of George Stephenson, father of Robert. Essay comprises of 14 hand-written pages numbered from 1 to 13 (missing one page) and beginning with 'The two separate blast pipes in the Rocket…'.
The two separate blast pipes in the Rocket were both contracted. The effect of the blast seems to be attributed by some to the union of the two pipes into one – nothing can be more fallacious for the first blast pipe that ever was made had the two combined into one, for the eduction pipe lay longitudinally upon the boiler, parallel with the centre line of the Engine into which single pipe the eduction steam
from both cylinders was discharged previous to reaching the chimney. Here therefore in the very first Engine a single blast pipe was used – Then How therefore can it be said that Hackworth in 27 invented the tapering blast pipe by combined the two into one – All the Engines which had been made up to that time had only one blast, the two were combined into one. – I I believe the whole misconception arises
from the fact that about 1827 Hackworth constructed an Engine with the cylinders outside the boiler x one on each side - the eduction steam therefore was carried towards the chimney by two separate pipes where they were joined after having entered the chimney The construction of the eduction pipes in the Rocket the cylinders being also placed on opposite sides of the
Boiler were carried towards the chimney in the same manner but instead of being united into one after passing thro’ the sides of the chimney they were turned up separately & contracted very considerably. The modern blast pipe would do just as well if it were divided into two as was done in the Rocket, but now that the positions of the cylinders are horizontal
and generally lying close together, it is obviously more simple to join the eduction pipes into one xxxx than to keep them distinct, and in addition to this it is obvious probable that the jet of steam is rather more efficient when brought into the exact centre of the chimney than when out of slightly on one side but this difference is certainly not very important at all events the Rocket acted efficiently with
the blast pipes so placed which I firmly believe was not modified until some time after the trials at Rainhill – but on this point xxxx it may also be stated that several Engines were made under my own direction in the Newcastle Factory where the blast pipe had the only the appearance of one, being in reality too two separate blast pipes in one casting. These Engines acted with just as much efficiency as those with
a combined blast pipe. This form of blast pipe was devised by for the purpose of ascertaining whether any and what amount of back pressure took place on the piston as consequence of the two eduction pipes being united in one – It No appreciable difference existed, so the separation between the two was therefore discontinued but it may be mentioned that since careful indicator cards have been
taken from Locomotive Engine a small but very distinct indication is recorded upon the line of pressure for the back of the piston which clearly shews that the pressure from the eduction steam from one cylinder is felt perceptibly perceptible upon the piston of the other altho [sic] experience undoubtedly shows that it does not amount to an imperfection worthy of consideration. The fact however that Engines have been made xxxx
with the as than / with the double blast pipe brought out it as nearly as practicable into the centre of the chimney shews distinctly that there is no substantial advantage but only a convenience is obtained by bringing two blast pipes into one. rather than But let us suppose that there is a great advantage in such an arrangement. What does it amount to all the Engines on the Killingworth, Hetton & Darlington Railways had this identical and system
long before Hackworth’s friends prentend to his having adopted it this system; the real fact I believe being that he may have the contacted it some there been the first the to contract it, more than George Stephenson did, but as I said in my former notes, supposing this to be the fact, now that the Boilers are so increased in their capacity for generating steam and the velocity of the piston so vastly augmented the contracted blast pipe
has been become inexpedient and almost wholly abandoned where high speeds are employed.
In conclusion let us suppose that Hackworth really did first construct the blast pipe, does not that at all effect [sic] the claim of George Stephenson to have been the first discoverer of the fact that throwing the eduction steam in the form of a vertical jet into the chimney greatly increased the power of the Locomotive Engine.
As well might it be contended that James Watt has no merit for his improvement in the steam Engine, because the effective performance of the steam Engine has been very greatly improved since his death. – The value or importance of an invention is not to be valued by it the results effects which are immediately produced but by those the xxxxx sequence that for there which generally flow from them. but in the case of the blast pipe we have seen that
other circumstances have attended the progress of the Locomotive Engine which nearly renders the contraction of the blast pipe comparatively unnecessary & in some cases positively objectionable.
I think it perfectly needless to go into the absurd and ridiculous stories which some of the writers have hatched up about my father’s conduct at with the Rocket at Liverpool – I had charge personally of the Engine myself with Ralph Hutchinson my father xx did not
really attend much to the Rocket and whatever was done to the Engine was done under my own eye & direction.
As regards any alterations being made by my father in consequence of any conversations between him and Hackworth after the arrival of the Rocket I utterly deny it - It was quite unnecessary for my father to talk to Hackworth about the form of his blast pipe because I knew what it was exactly and I preferred my own arrangement at the time.