Manchester line, horses were out of question. The debatable ground being thus narrowed, how was the remaining point to be decided? Was a capital of £100,000 to be invested in stationary engines, or were locomotives to be adopted?'

Whilst this question was under discussion, and for several months preceding the October trip just mentioned, Robert Stephenson had been racking his brains to settle another and much more important matter - How to improve the locomotive? how to increase at the same time its power and speed? It was as clear to him, as it had been to his father, that above all things it was requisite. to increase in the locomotive the capability of rapidly generating steam. Sufficient heat, with adequate means for rapidly applying that heat to the water, was the desideratum. Eventually the multitubular boiler and the steam-blast of the Rocket' gave the required conditions; but previous to their attainment, Robert and his father made numerous failures in attempting to build a really satisfactory travelling engine.

To increase the heating surface, they introduced into the boilers of two engines made for the St. Etienne Railway small tubes that contained water; but the scheme was futile-the tubes soon becoming furred with deposit and burning out. In other engines they with the same object inserted two flues, each with a separate fire. On this principle was constructed The Twin Sisters' -the name being suggested by the tubes. A third method adopted was to return the tube through the boiler. A fourth plan- in which may be perceived a nearer approach to the multitubular system was adopted in a boiler made, at the beginning of 1828,

6

with two small tubes branching off from the main flue. The sketch for this last engine was sent from Liverpool by George Stephenson to his son on January 8, 1828, and in the postscript the sanguine father says

The small tubes will not require to be so strong as the other parts of the boiler, and you must take care that you have no thick plates and thin ones, as is often the case with those which come from Bedlington. You must calculate that this engine will be for all the engineers in the kingdom - nay, indeed, the world

to look at.' During his residence at Liverpool, George Stephenson had the great advantage of close personal intimacy with Mr. Booth, the treasurer of the Liverpool and Manchester Railway. Mr. Booth was not only an enthusiastic advocate of the locomotive, but he had a strong natural taste for mechanics, and would probably have distinguished himself had he made engineering a pursuit instead of a pastime. As it is, the multitubular boiler, as a practical agent, must be attributed to him, whatever may be the merit due to such claimants as M. Seguin and Mr. Stevens. Mr. Booth was consulted on all the plans introduced by the Stephensons, and his name continually appears in the letters which passed between the father and son. Writing to Robert, on January 31, 1828, George, referring to the experiment then in hand, says-With respect to the engine for Liverpool, I think the boiler ought not to be longer than eight feet. The engine ought to be made light, as it is intended to run fast. Mr. Booth and myself think two chimneys would be better than one, say eight inches in diameter and not to exceed fifteen feet.' In conclusion the father adds I trust the locomotive engine will be pushed.

Its answering is the most important thing to you, and recollect what a number we shall want I should think thirty.'

On April 15, 1828, George Stephenson, still sanguine as to the result of the boiler with diverging tubes, wrote to Robert

I am quite aware that the bent tubes are a complicated job to make, but after once in and well done it cannot be any complication in the working of the engine. This bent tube is a child of your own, which you stated to me in a former letter. The interior of a watch looks complicated, but when once well fit up, there needs very little more trouble for one hundred years, and I expect the engine you are fitting up will be something similar to this watch with respect to its working parts.

Five days later George Stephenson, with regard to this same engine, wrote a letter to his son, which is important, as it bears on a question that has been a subject of much warm controversy amongst engineers.

Liverpool: April 20, 1828.

DEAR ROBERT,—I duly received yours dated the 16th inst. I do not think there can be much difficulty in cleaning the refuse matter of the fire from the locomotive-engine boiler. I would make the nozzle pipe that goes in from the blast to be a kind of grating rather than of a conical shape, and to project about two feet into the fire. The grating to be on the upper side. The nozzle piece to be made with a flange, fitting very nicely to the plate at the front of the fire to prevent the escape of air, and kept on by a bolt and cotter, or two screw-bolts. This nozzle piece could easily be taken out at any time and the fire cleaned at the hole. This I think may be done while the engine is working upon an easy part of the road. It appears to me it will be found better to feed one time with coke and the next with coal. I think the one would revive the other.

I do not think there can be so much difficulty in firing on this plan as on the old one.

If

you wish me to see the boiler tried before it is put into its seat I will endeavour to come.

If this new engine is found to answer, it will be the best way to alter all the Darlington engines to the same plan. By doing so the last engine will not be found too heavy for the road.

This engine with the bent tubes, like other attempts made in that year to improve the locomotive, was a failure. Time was running short; the period for opening the new line was fast approaching, and yet George Stephenson and his son had not hit on the way to build such an engine as should sweep the ground from under the advocates of stationary machines.

Writing from Liverpool to Mr. Longridge at the close of the year 1828, Robert communicated the success attending the result of his new boiler made to burn coke.

Liverpool Railway Office: Dec. 1, 1828.

MY DEAR SIR,- It was arranged that I should leave this place to-morrow, but the directors of the Liverpool and Manchester have resolved to-day that my father and I are to meet the deputation which was recently in the north, and enter into detailed calculations relative to the much-contested question of locomotive and stationary engines. Since I wrote you last we have had my new boiler tried at Laird's Boiler Manufactory in Cheshire. You are probably aware that this boiler was made to burn coke. The experiment was completely successfulindeed, exceeded my expectations. Six of the directors went the other day to witness a second experiment. They were all perfectly satisfied. The enemies to the locomotives . . . . said the experiment had answered to the fullest extent. The boilers were shipped to-day in the steam-boat viâ Carlisle, from which place they will be forwarded to Newcastle. . . . . I have had two letters from Forman about the locomotive engine, and he has given us the order at last, but nothing can be done to it until I reach the manufactory.

I am really as anxious to be at Newcastle again as you can be to see me. I cannot say that I like Liverpool. Do not answer

-'s letter until I see you, as he has left me one also, full of such close queries on engineering that I rather hesitate giving him the information in such an offhand manner as he calculates upon.

I am much pleased that you are interesting yourself in the suit of Locomotive versus Stationary. It is a subject worthy of your aid and best wishes; but you must bear in mind, wishes alone won't do. Ellis has got settled, and I have got up a proposal in my father's name, which is now before the directors of the Canterbury Railway Co. I expect at a general meeting next Thursday, which will be held at Canterbury, they will decide upon it. I cannot explain it fully in a letter, and therefore defer it till I see you. I have thanked Mr. Booth as you requested.

In January 1829, Mr. James Walker, then of Limehouse, and Mr. James Urpeth Rastrick, then of Stourbridge, were commissioned by the Liverpool and Manchester Railway directors to visit Darlington and the Newcastle country, and report to them on the advantages and disadvantages of the locomotive system. Mr. Walker and Mr. Rastrick were practical engineers of high reputation; and they conscientiously discharged the duties which they undertook. The task assigned them was not to argue on the possibility or probability of speedy improvements in the locomotive. They were to inspect the travelling engines, observe their capabilities, and judge them as they were, not as they might or would be. On the Stockton and Darlington line the two commissioners found locomotives travelling at paces varying between four and six miles an hour. An engine weighing, with its tender, fifteen tons, would drag twenty-three and a half tons' weight of carriages, containing forty-seven and three-quarters tons of goods, at the rate of five miles per hour. So much, and no more, could the locomotive of