Any party whose tenders may be accepted, shall, if required, furnish forthwith a more detailed drawing and specification of the engines as they propose to furnish them; the specification and drawing now sent being expressly made very general, in order that each manufacturer may, so far as is consistent with the general requisites and conditions, adopt his own methods of construction, or use any existing patterns.

The economical character of the engines which Mr. Brunel desired to obtain is sufficiently indicated by the requirement that they were to be high-pressure condensing engines, fitted with double-seated expansion valves, and having boilers proved to 100 lbs. per square inch, and guaranteed to work with safety valves loaded to 40 lbs. per square inch.

The tenders accepted were those of Messrs. Boulton and Watt, Messrs.

Rennie, and Messrs. Maudslay and Field.

Mr. Brunel left it to the contractors to prepare their designs without any interference on his part, deeming it best to rely on their unfettered judgment.

The task of manufacturing and fitting the cast-iron tube was one of some difficulty, the longitudinal slit allowing of considerable distortion in the casting. This work was undertaken by Mr. George Hennett, by the aid of a set of very effective tools devised by Mr. T. R. Guppy.

The tubes were supplied at the rate of one mile per week, and by the middle of 1846 nearly the whole line was laid to Newton, and the valve was ready to be fixed.

In the autumn of 1846, Mr. Joseph Samuda went to Dawlish, taking with him a staff of a.s.sistants trained in the working of the system at Croydon; and every effort was made to advance the completion of the engines and the other parts of the apparatus.

Owing, however, to vexatious delays in the erection of the engine-houses and engines, it was not until the commencement of 1847 that a piston-carriage was able to traverse the first six miles out of Exeter.

And, though repeated experimental trains continued to be run, no pa.s.sengers had been conveyed by Atmospheric trains prior to the general meeting of the shareholders, at the end of August. Mr. Brunel's report on this occasion was as follows:--

August 27, 1847.

It is a subject of great regret, and to no one more than to myself, that we have as yet been unable to open any portion of the line to the public with the Atmospheric apparatus, although a considerable distance has for some months been in a state to admit of frequent experiments being made upon it. This delay has arisen princ.i.p.ally, if not entirely, in that part of the whole system which it might have been expected would have been the least exposed to it--namely, the construction and completion of the steam-engines.

It is due to Mr. Samuda that I should say that, so far as regards the mere pipe and valve, and other details which may be said to const.i.tute the Atmospheric apparatus, we might long since have commenced. But the engines, although designed without any interference with their plans, and furnished by the best makers of the country, and although differing so slightly from the ordinary construction of steam-engines, have proved sources of continued and most vexatious delays, both in the unexpected length of time occupied originally in their erection, and in subsequent correction of defects in minor parts. While the engines were imperfect, it would not only have been unwise to have commenced working the line, even had it been practicable, but the frequent interruptions to the continuous working of all the engines rendered it impossible to complete and test the different portions of the Atmospheric apparatus. There are still some defects to be remedied in one or two of the engines, and I am using every endeavour, by persuasion and by every other means in my power, to urge on the manufacturers in their work of completion. Within the last week or two only have we been able to work at all continuously between Exeter and Teignmouth, so as to have the opportunity of trying the different parts, and getting the various details requisite for actually working trains tested and brought to sufficient perfection to ensure efficiency and regularity.

Since the beginning of last week, however, four trains per day have been run regularly, stopping at the stations, and keeping their time as if working for traffic. The tube and valve appear in good order, and the whole has worked well, but the running in this manner can alone show the deficiencies which may still exist in the details necessary for stopping, and starting quickly from the stations, and all the other minor operations incidental to working the traffic in the ordinary course; and, until all these arrangements are completed, and the engines in more perfect order, I think it would be much better to defer at least the subst.i.tution of the Atmospheric for the locomotive working. Trains, in addition to those now running may perhaps be advantageously worked for the public, after a further short continuance of the present practising.

The two engines completing the number to Newton are nearly ready for trial, and it is to be presumed that, after the experience of the past, the makers will be enabled to put them at once into an efficient state.

The delays and difficulties attending the bringing into operation the Atmospheric System upon this portion of the railway have been beyond all antic.i.p.ation, and beyond what any previous experience would have justified anybody in antic.i.p.ating. The difficulties have all been seriously aggravated by the necessity (consequent, certainly, upon the original delays) of working the line with locomotives during the construction and completion of the Atmospheric apparatus. Not only has the constant occupation of the line interfered with the progress of the work, but it has been necessary to devise all the arrangements so as to admit stations, sidings, and line being worked either by locomotive or by Atmospheric in succession, or even at the same time.

These difficulties, added to those always consequent upon the introduction of any new system, have been most wearying and incessant, and I am not surprised that the public and the proprietors should have been impatient. I trust the ultimate result will remove any grounds for disappointment.

The stress of personal anxiety and personal fatigue, experienced by Mr.

Brunel and by all who were engaged in the work, was very severe, and continued so to the end. Not only was the progress in the completion of the work slow, but in spite of every exertion the results were incessantly marred by unfortunate contingencies which involved further delay, discouragement, and expenditure. Moreover, the reaction which followed the railway mania had set in; calls were ill responded to, and great difficulty was experienced in raising the money requisite for the completion of the line.

Under these circ.u.mstances it was resolved, on September 1, not to incur any new expenses in relation to the Atmospheric System beyond Totness, and to limit any expenditure already contracted for, until its working between Exeter and Totness had been fairly tried, except to provide a.s.sistant power up the two inclines.

On September 8 the Atmospheric trains began to take their share in the pa.s.senger duty of the line, four trains running each way daily; and, except when occasional mishaps caused delay, the new mode of traction was almost universally approved of. The motion of the train, relieved of the impulsive action of the locomotive, was singularly smooth and agreeable; and the pa.s.sengers were freed from the annoyance of c.o.ke dust and the sulphureous smell from the engine chimney.

In other respects the record of progress is but a chequered one, and exhibits, in spite of great and able efforts and brightening intervals of occasional improvement, indications of growing difficulties deepening into ultimate defeat.

In examining the chronicle of events which correspondence and memoranda supply, it is inevitable that references to failure and disaster should be found relatively in far greater abundance than records of success; and this for the simple reason that there was at that time great use in taking note of the unfavourable incidents that occurred, almost none in mentioning successful work.

There is therefore some danger of falling into a mood of unjust depreciation, such as Mr. Brunel had in energetic terms urged the Directors to guard themselves against. He protested against their requiring (as they once intended to do)--

continuous and detailed reports--if true and honest, of course containing nothing but accounts of mishaps--of a system which (he says) we are struggling to render perfect. Why, a daily account of our locomotive mishaps would ruin the locomotive system, if it were new! I will undertake to say that the mishaps of yesterday or to-day on the Great Western Railway were as great as that of Tuesday on the South Devon.

The Atmospheric System was vaguely credited with every delay which a train had experienced in any part of its journey; though, in point of fact, a large proportion of these delays was really chargeable to that part of the journey which was performed with locomotives. It often happened that time thus lost was made up on the Atmospheric part of the line, as is shown by a record of the working, which is still extant. In the week, September 20-25, 1847, it appears that the Atmospheric trains are chargeable with a delay of 28 minutes in all; while delays due to the late arrival of the locomotive trains, amounting in all to 62 minutes, were made up by the extra speed attainable on the Atmospheric part of the line.

Not unfrequently, however, casualties occurred; due indeed to remediable causes, but yet of discouraging aspect in themselves, and deriving additional weight from the manner in which they reacted on the cost of working. Such, for instance, were the frequent and occasionally very serious breakages in essential parts of the pumping-engines. Again, the cupped leathers of the travelling-piston, which made it air-tight, were often destroyed while it was pa.s.sing the various inlet and outlet valves. Improvements in the valves were introduced to meet this difficulty; but the remedy could not be applied at once throughout the line, and much inconvenience was thus experienced, and a considerable expense incurred. Another source of inconvenience was the water which at times acc.u.mulated within the tube.

In many respects the results which had been calculated on were realised, and the new arrangements necessary to the working of the system were successfully brought into operation.

The speed of the trains corresponded fully with the degree of vacuum obtained; that is to say, the train resistances proved to be what had been antic.i.p.ated.[69]

After the trial of a great variety of air-pump valves, a form was adopted which was found to answer exceedingly well.[70]

In the Atmospheric tube, the system of self-acting inlet and outlet valves, by which the piston was enabled to leave the tube on approaching a station and enter it again on recommencing its journey, were, on the whole, successfully adapted to their duty.

Again, an arrangement for starting the train rapidly from the station, without the help of horses or of locomotives, had been brought practically into operation. This arrangement consisted of a short auxiliary vacuum tube containing a piston which could be connected with the train by means of a tow-rope, and thus draw it along till the piston of the piston carriage entered the main Atmospheric tube. Some accidents at first occurred in using this apparatus, but its defects were after a time removed; and it is hardly to be doubted that the various minor difficulties of the Atmospheric System could soon have been effectually mastered.

It now remains to show how it was that, in spite of much that was hopeful, a vigorously sustained contest ended in defeat, instead of being prolonged into victory.

In working the Atmospheric System on the South Devon Railway grave difficulties were throughout encountered, for which to the last only imperfect remedies could be found.

As regards the power consumed, the engines of each pumping station worked up to about 236 indicated horse-power, and their regulated duty for each train, including the antic.i.p.atory pumping, was equivalent to 55 minutes of work for every mile of the length of tube they had to exhaust. As the running speed averaged 40 miles per hour, or a mile in 15 minutes, the 236 horse-power during the 55 minutes of pumping must be regarded as equivalent to 865 horse-power during the actual pa.s.sage of the train. Now, making full allowance for piston friction and extra friction on curves, for the power expended in getting up speed, for the excess of air-pump resistance due to the changes of temperature experienced by the air under exhaustion, and even for the very large actual amount of friction in the engines employed, the work done should have been represented by an expenditure of 240 horse-power during the pa.s.sage of the train. If to this is added an allowance for leakage, such as the experiments at Dalkey indicated would be amply sufficient with the longitudinal valve in good condition, it may be said that Mr.

Brunel had a right to expect that the duty would be performed with an expenditure of 300 horse-power; whereas it actually required 865 horse-power, or nearly three times the amount.

The explanation of this waste is simple.

Serious and unexpected causes of failure developed themselves in the longitudinal valve, and led to an excessive amount of leakage. A great part of the normal duty of the engines was, as has been stated, to exhaust the tube previous to the entry of the train; and when, owing to leakage, the amount of air to be so pumped out was greatly increased, it became necessary that the operation should be commenced much earlier.

There was thus a longer time during which the leakage could take place, and a still greater amount of air to be pumped out. It therefore followed that a large increase of leakage involved waste of power in an enormously increased proportion.

The length of time occupied by the antic.i.p.atory pumping was often increased by the difficulty of arranging proper telegraphic communication on the South Devon Railway, and by the absence of it on the Bristol and Exeter Railway. The Electric Telegraph was in its infancy, and though Mr. Brunel had been the first to apply it in connection with railways, namely, between London and Slough on the Great Western Railway in the year 1839, it was not brought into perfect working order on the South Devon Railway till the Atmospheric System was on the point of being abandoned. The result of the defects in the telegraph was that, when a train was late, warning was not received at the several engine-houses;[71] and thus, when this was the case, the pumping-engines which had been started at the right interval of time before the train was due, had to be kept at work for a needlessly long period pumping out the air, which was all the while leaking in through the deteriorated valve. This inefficiency of the telegraphic apparatus would have been of trifling importance but for the defects of the valve.

Had the valve been as perfect as it was expected to be, the vacuum, after it had been formed, could have been maintained by an expenditure of power very moderate in comparison with that which was actually required.

As regards the relative cost of the power consumed, it appears that, owing to imperfections in the engines, their expenditure of fuel per indicated horse-power was more than double that of the best of the Cornish pumping-engines, to which they were a.n.a.logous; while the cost of working was more than three times as great.

The defects in the engines were for the most part such as might have been remedied; and this would have been done, had not the excessive duty imposed on them by the leakage of the longitudinal valve prevented their being stopped for repairs and alterations. In this way the defects of the different parts of the apparatus mutually aggravated each other.

It appears then that, chiefly owing to the defective longitudinal valve, the engines were expending nearly three times the power which they should have done for a given tractive duty, according to previous experience, and the results obtained on the Dalkey line, and that they cost per horse-power at least three times as much as was expected.

The cost of traction, nearly nine times as much as had been calculated on, was between two and a half and three times what it would have been with locomotive power; and this was on a level part of the line, where the comparative advantages of the Atmospheric System were not exhibited as they would have been in the part which had steep gradients.

The imperfections of the longitudinal valve have now to be described. By its condition the Atmospheric System had to stand or fall. With an efficient valve, the defects of the other parts of the apparatus would have been of minor importance, and time would have been given for remedying them. When the leakage became considerable, the defects of the telegraph and the defects of the engines alike a.s.sumed a formidable aspect.

The failure of the valve was due, partly to the composition which was used to seal the joint where it opened, and partly to the material of which the valve consisted. The difficulty of obtaining a suitable composition was the first which had to be encountered. On the South Devon a lime soap was eventually found to answer the purpose well. Its surface, however, from exposure to light and air, formed into a hard skin; and to remedy this a thinner and more fluid material, a compound of cod-oil and soap, was laid on to keep it soft. This answered satisfactorily, but it required frequent renewal, as it was apt to be drawn into the tube by the rush of air when the valve was opened. The renewal of the various compositions, and the careful examination and repair which the valve constantly required, was a cause of great anxiety and expense.

But in the materials of the valve lay the source of the more serious difficulty.

The ready affinity of leather for oil and grease, and its suppleness and closeness of grain when saturated with substances of that nature, had long been known and utilised. It had not been antic.i.p.ated how readily, with air-pressure on one side and a partial vacuum on the other, the oily matters with which the leather was charged would escape from it, especially in the presence of water. Although, while the leather was saturated with water, the valve was remarkably air-tight; when frost supervened the water became frozen, and gave a fatal stubbornness of texture, which rendered the valve incapable of closing properly. Again, in long-continued drought the leather became intractable from its dryness; and the stiffening, whether from frost or drought, rendered it liable to be torn. An immediate application of seal-oil penetrated the leather, and relaxed its stiffness; but the remedy often could not be applied in time, and, moreover, was expensive.

A still more grave defect was all the while becoming matured, and was undermining every hope that a suitable dressing could be discovered, and that the longitudinal valve might be made perfect.