Origin of the Ordinary Gauge of Railways—Adoption by Mr. Brunel of the Broad Gauge on the Great Western Railway—Reasons for its Adoption
The railways designed by Mr. Brunel were, with a few exceptions, distinguished from those in all other parts of England by a peculiarity in the width between the two rails forming each line of way, or in what is called the gauge. In most railways, the distance between the internal edges of the rails is 4 feet 8½ inches, being what is termed the narrow gauge; on Mr. Brunel’s railways, it was seven feet, or what is termed the broad gauge.
The gauge of the earlier railways, which were but a modification of the old wooden tramway, was made that of the tram plates which they superseded; and this had been originally fixed to suit the distance between the wheels of the country carts in the north of England.
When Mr. George Stephenson introduced the locomotive engine, the gauge of the lines in the Northumberland district had been already fixed. In laying out the Stockton and Darlington line (1821-1825) he saw no reason to depart from the gauge he had previously adopted; and, indeed, some of the waggons to be used on this line were brought from the Northumberland collieries. In this way the first important railway in England was made with the gauge of 4 feet 8½ inches; not from a deliberate choice of this width on the ground of any peculiar advantages, but from the mere fact of its already being established elsewhere.
In the construction of the Manchester and Liverpool Railway, in 1826, the same gauge was adopted as on the Stockton and Darlington; this course was also followed by the Grand Junction and the London and Birmingham Railways, and thus the 4 feet 8½ inches gauge became established in that part of the country.
Long experience appears to have determined the general type of wheeled vehicles: the wheels being of somewhat large size, and the body placed between them, so as to come down close upon the axle-tree.
This type, which gives obvious advantages in a mechanical point of view, appears to have been adhered to in all railway vehicles used before the opening of the Liverpool and Manchester Railway; these, however, were chiefly coal-waggons. But on the Liverpool and Manchester Railway it was soon perceived that the great increase of carrying power which the railway afforded must be met by a corresponding increase of space in the rolling stock, as it was necessary to accommodate light bulky goods and passenger traffic. The available width between the wheels was limited to about 4 feet 6 inches, and to carry in this width any large amount of cotton goods, or of passengers, would have required a train of an inordinate length. To meet this difficulty a new form of vehicle was designed; the wheels were made small, and the body was raised and widened out, projecting on either side over the tops of the wheels.
The earliest description of this form of waggon is contained in the second edition of Wood’s ‘Practical Treatise on Railroads,’ published in 1832, about two years after the opening of the Liverpool and Manchester Railway. In Plate III., Mr. Wood shows a truck with a raised platform overhanging the wheels, and adapted for carrying loose boxes of coals; adding, in the description:
Although the drawing shows only the form of boxes used for the conveyance of coals, yet it will readily occur that the form can be varied to suit the carriage of any kind of articles; the framework or body of the carriage being raised above the wheels, the breadth can be extended to any width which the distance between the railways will admit.
Such was the state of matters when, in the year 1833, Mr. Brunel was appointed Engineer of the Great Western Railway. With the view of leaving the question of gauge open for future consideration, he procured the omission in the Great Western Act of a clause defining it. He came to the conclusion that it would be desirable to adopt a wider gauge, and he recommended this measure to the Directors in a report dated October 1835. 
In October 1836 a Royal Commission, consisting of Mr. Drummond, Under-Secretary for Ireland, Mr. R. Griffith, Colonel (now Field-Marshal) Sir John Burgoyne, R.E., and Professor Barlow, of Woolwich, was appointed to report on the establishment of railways in Ireland. They considered carefully the question of gauge, and their arguments in favour of an increase in the gauge were afterwards stated by Mr. Brunel to be identical with his own.
They drew attention to the advantage of large wheels, the use of which would be facilitated by a wider gauge; and they thought it a matter of importance to be able to place the bodies of the carriages between the wheels, instead of over them.
It was the width of the carriages, and not the distance between the rails, that determined the general dimensions, and therefore the cost, of the works of a railway. Mr. Brunel saw many advantages to be gained by an increase in the gauge, even while retaining the existing dimensions of carriages; and he thought it unwise at the commencement of a work of such magnitude as the Great Western Railway to retain a limit the inconvenience of which had already become apparent.
He says, in his evidence before the Gauge Commission:
Looking to the speed which I contemplated would be adopted on railways, and the masses to be moved, it seemed to me that the whole machine was too small for the work to be done, and that it required that the parts should be on a scale more commensurate with the mass and the velocity to be attained. (Q. 3924.)
The width between the rails being the fundamental dimension of ‘the whole machine,’ on which its entire development must depend, Mr. Brunel proposed to begin by the enlargement of this dimension, and recommended that on the Great Western Railway the gauge should be seven feet. He considered that the whole of the parts of the railway and of its rolling stock would be susceptible of continual, though gradual improvement, and that it was highly advisable to remove, in the outset, a great obstacle in the way of this progress.
He did not in the first instance propose any important change in the details as consequent on the wider gauge; and in regard to one of the principal points, the diameter of the wheels, he said:—
I am not by any means prepared at present to recommend any particular size of wheel, or even any great increase of the present dimensions. I believe they will be materially increased; but my great object would be in every possible way to render each part capable of improvement, and to remove what appears an obstacle to any great progress in such a very important point as the diameter of the wheels, upon which the resistance, which governs the cost of transport and the speed that may be obtained, so materially depends. (Report in Appendix I)
Mr. Brunel also looked forward to the advantages which a wider gauge would give for the construction of the locomotive engines. Difficulties had been already experienced from the limited width between the wheels, which cramped the machinery, rendering it difficult of access for repairs; it also limited the size of the boiler and fire-box, on which the power depended. For this reason Mr. Brunel considered that a wider gauge would present great advantages, as it would allow the locomotives to be constructed of greater power, and with their machinery arranged in a more advantageous manner. He also thought that the greater width of base for the carriages would give increased steadiness and smoothness of motion, with greater safety, particularly at high speeds, and that there would be the advantage of being able to use larger wheels for the carriages. Moreover, he had in view the possibility which the broad gauge would give of adopting wheels of a still larger diameter without raising the centre of gravity, the body of the carriage being placed between them, as in the original type of common road vehicles.
The broad gauge was also considered by Mr. Brunel in prominent connection with the peculiarly favourable circumstances of the Great Western line, in regard to its gradients and curves. He thought that ‘it would not have been embracing all the benefits derivable from the gradients of the Great Western Railway, unless a more extended gauge was adopted.’ In the first place, it was evident that a diminution of the frictional resistance would present the greatest advantage where the gradients were flat. In regard to curves, the wider gauge was at that time considered by him to be more advantageously applied where the curves were of large radius than where they were sharp.  On the Great Western Railway both gradients and curves were remarkably good; with the exception of two inclines of 1 in 100, on which auxiliary power was proposed to be used, there was no gradient between London and Bristol steeper than 1 in 660, the greater part of the line being nearly level, and except between Bath and Bristol there was no curve sharper than about one mile radius.
For these reasons Mr. Brunel thought that unusually high speed might easily be attained for passengers, and great tractive power for goods. He said:—
I shall not attempt to argue with those who consider any increase of speed unnecessary. The public will always prefer that conveyance which is the most perfect, and speed, within reasonable limits, is a material ingredient in perfection in travelling. (Report in Appendix I)
In deciding that the distance between the rails should be seven feet, Mr. Brunel seems to have been guided by the principle that the wheels should be put sufficiently far apart to admit of an ordinary carriage body being placed between them. 
Mr. Brunel did not anticipate that the difference between the gauge he proposed and that of other railways would lead to any important inconvenience. The views he held on this subject were expressed fully by him in a report of December 13, 1838. He says, speaking of the difficulty of communication between the Great Western and other railways:—
This is undoubtedly an inconvenience; it amounts to a prohibition to almost any railway running northwards from London, as they must all more or less depend for their supply upon other lines or districts where railways already exist, and with which they must hope to be connected. In such cases there is no alternative.
The Great Western Railway, however, broke ground in an entirely new district, in which railways were unknown. At present it commands this district, and has already sent forth branches which embrace nearly all that can belong to it; and it will be the fault of the company if it does not effectually and permanently secure to itself the whole trade of this portion of England, with that of South Wales and the south of Ireland; not by a forced monopoly, which could never long resist the wants of the public, but by such attention to these wants as shall render any competition unnecessary and hopeless. Such is the position of the Great Western Railway. It could have no connection with any other of the main lines, and the principal branches likely to be made were well considered, and almost formed part of the original plan; nor can these be dependent upon any other existing lines for the traffic which they will bring to the main trunk.
Mr. Brunel was not singular in holding the opinion that it would be desirable to allot a given district to one railway, which might conveniently serve it by means of a trunk line and branches of a special gauge. In the Eastern Counties line, designed in 1836, by Mr. Braithwaite, and opened in 1839, a gauge of 5 feet was adopted; and Mr. Robert Stephenson, as engineer of another line, the Northern and Eastern Railway, branching out from the Eastern Counties to the northward, adopted the same gauge. It was not till the Northern and Eastern line was extended, some years afterwards, that the rails of the whole system were altered to the narrow gauge.
Mr. Brunel’s recommendation was adopted by the Directors of the Great Western Railway; and, in their report of August 25, 1836, after observing that the generally level character of the line would greatly facilitate the attainment of a higher speed of travelling, they pointed out the advantages of the broad gauge, and stated that engines had been ordered specially adapted to the nature of the line, which would be capable of attaining with facility a rate of from thirty-five to forty miles per hour.
The line was opened between Paddington and Maidenhead on June 4, 1838, and the performance of the engines was considered satisfactory, trains of eighty tons and upwards being drawn at speeds of from thirty-eight to forty miles per hour.
Notwithstanding these favourable results, the change in regard to the gauge did not pass unquestioned. Attacks were made on it in various quarters, and considerable excitement was caused among the shareholders and the public.
It was asserted that the width of 4 feet 8½ inches was exactly the proper width for all railways, and that a deviation from it was tantamount to the abandonment of an established principle which experience had proved to be correct. It was further alleged that the cost of all the works connected with the formation of the line would be greatly increased; that the carriages must be stronger and heavier, that they would not run round the curves, and would be liable to run off the rails, and particularly that the increased length of the axles would render them liable to be broken. These were not advanced as difficulties which, existing in all railways, might be somewhat increased by the increase of gauge, but they were assumed to be peculiar to the broad gauge, and fatal to it. Some urgent representations appear to have been made to the Directors; for in their report of August 15, 1838, they state, that as the gauge and the permanent way, which had also been the subject of adverse criticism, had been sources of some anxiety to them, they had applied to three of the most eminent authorities on the construction and working of railways—Mr. James Walker, President of the Institution of Civil Engineers, Mr. Robert Stephenson, and Mr. Nicholas Wood, of Newcastle-on-Tyne—to undertake a thorough inspection of the line, to investigate the working of it, and to give their opinion on the plan adopted.
Mr. Walker and Mr. Stephenson declined the task, on the ground that they did not wish to become embroiled in professional controversy, but Mr. Wood undertook it; and a similar commission was afterwards given to Mr. Hawkshaw.
In order to put the shareholders fully in possession of all the information in their power, the Directors published a very complete statement by Mr. Brunel on the arrangements adopted by him. It will be seen that in this report, which is given in Appendix I. p. 525, he states his original arguments, and answers the objections brought against his plans; and he contends that the result of experience establishes their success. In regard to the gauge, he says:—
Everything that has occurred in the practical working of the line confirms me in my conviction that we have secured a most valuable power to the Great Western Railway, and that it would be folly to abandon it.
But the two engineers, to whom the consideration of this matter had been referred, differed materially in opinion from Mr. Brunel. The nature of their investigations and reports, and of Mr. Brunel’s replies, is stated in the extracts given below from the report of the Directors in January 1839.
 No copy of this report can be found; but documents of subsequent date sufficiently indicate the nature of the arguments Mr. Brunel used in it.
Mr. Brunel had about this time given much attention to the principles of wheel carriages, as is manifested by an interesting article ‘On Draught’ written by him for the work on ‘The Horse,’ published by the Society for the Diffusion of Useful Knowledge. With regard to this point, Mr. Brunel afterwards admitted that he had held a mistaken opinion. In speaking of his reasons for adopting the narrow gauge on the Taff Vale Railway in 1838, he said before the Gauge Commission:—‘One of the reasons, I remember, was one which would not influence me now; but at that time I certainly assumed that the effect of curves was such, that the radius of the curve might be measured in units of the gauge, in which I have since found myself to have been mistaken.’  See Mr. Brunel’s report of August 1838, printed in Appendix I.
This plan was never adopted, as it was found desirable upon the broad gauge to use still wider carriages overhanging the wheels; but advantage was taken of the broader base to use wheels of greater diameter. However, in the saloon carriages, where ease of travelling was the chief object aimed at, the bodies were placed within the wheels.