To ascertain this, the time tables of the several companies having fast or express trains were examined, and the returns furnished by those companies of the actual speeds attained by the express trains, during 30 successive days from the 15th June to the 15th July 1845. The commissioners also travelled in the express trains, and noted the speed, mile by mile; the results of which showed that the average speed of the Great Western, both by express and ordinary trains, exceeded the highest speed of similar trains on any of the narrow gauge lines. But some of the latter have trains which exceed the speed of those on the recently constructed lines on the broad gauge; owing to the comparatively unfavourable gradients and curves. These remarks apply to the Bristol and Gloucester, and the Swindon and Gloucester. The inclination and curves on the Great Western between London and Bristol are particularly favourable for high velocities. And it is worthy of remark that in some portions of the narrow gauge lines, where the gradients and curves are very easy, that the speed attained was for a time above that on the Great Western. The difference of effect, according to the nature of the gradients, is shown in a very strong light by a comparison of the time occupied in passing over different portions of the Great Western line.
The speed-from Paddington to Didcot by the express train is 47 1/2 miles per hour; from Didcot to Swindon it is 41.1; from Swindon to Gloucester only 31. 7; from Swindon to Bath 48. 2; but returning only 37. 2; from Bristol to Taunton, the speed is 46. 3; and from Taunton to Exeter only 39. 2.
It is stated that the locomotive engines on the Great Western line have not been altered from the opening of the railway, (which was designed on the broad gauge in order to obtain higher velocities with equal safety,) while the recently increased speed on the narrow gauge lines has been acquired by the introduction of new engines of greater power; and the commissioners seem to think that they are now as powerful as they can probably be made on the narrow gauge; but that the broad gauge lines have still the means of augmenting the power, and hence the velocity of their engines, within the limits of the stability of roads, to bear such increased weight and motion. Since the introduction of express trains, the accidents arising from running off the line have been indeed more numerous within the last seven months, than within the five preceding years; and it is questionable whether this contest for speed ought to be carried to any greater length.
It is the opinion of several engineers, that it is the stability of the road, and not the power of the engine, that will prescribe the limits of safe speed.
"On the first introduction of passenger railways, speeds of about 12 miles per hour only were anticipated;" (which is difficult of comprehension, seeing that steam locomotives on the common road went faster,) the rails then employed weighed only 35lbs per yard, and the engines 6 or 7 tons. As soon as the speeds of 20 and 24 miles were attained, they found it expedient to increase the rails to 50!bs per yard, and the engines to 10 and 12 tons. Since that time the weights of the rails have been progressively increased from 65 to 851bs per yard, and the ordinary engines on the broad gauge to 22 tons: while those on the narrow are only 2 or 3 tons less, and some few more; one even of 30 tons, on six wheels. This increased weight has been chiefly obtained by lengthening the boiler (augmenting thereby the evaporating surface), and fixing the engine cylinders on the outside. In such engines as have by this elongation been made to overhang the fore and hind axles considerably, the position of the outside cylinders have had, it is said, a tendency to produce an irregular or rocking motion; causing them to be less safe at high velocities.
The commissioners are, however, of opinion, that this great length of engine is not essential to the attainment of high velocities on the narrow gauge lines. They timed the express trains on four different journeys on the South Western line, in both directions; that the whole distance was performed very satisfactorily in about 1 hour and 52 minutes, including the time of stoppages, being at an average of 4p miles per hour, on a line which, in one direction, rises for a length of more than 40 miles on a very prevailing gradient of 1 in 330; and in the oilier rises for several miles on a gradient of 1 in 250. On each occasion a distance of five miles, on a level part of the road, was passed at the rate of 53 miles per hour. The length of the engine boiler was only 8 ft. 7 inches, the driving wheels 6 ft. 6 inches in diameter; the leading wheels had both inside and outside bearings. The diameter of the cylinder in one case was 15 inches, in the others 14 1/4 inches, both outside, and attached to the smoke box.
In proceeding to compare the locomotive engines, the commissioners remark that the boilers of the narrow gauge have a smaller power of evaporation than those on the broad gauge; and that whatever may be the attempts to augment that power, it is clear that they may, in this respect, be surpassed on the broad gauge. It is, however, a current opinion that the engines on both gauges have nearly obtained that speed and power which it would be justifiable to employ, in reference to the present strength of the rails and the firmness of the earthworks.
The diameter of the driving wheels of the broad gauge engines exceeds that of the driving wheels of the narrow gauge engines, which circumstance is unquestionably favourable to high speed; because the steam is used to greater advantage, and because the alternating shocks upon the machinery are less rapid. The commissioners think, however, that at the speed of 40 miles an hour, the difference between the two engines may be trifling, but that at speeds of 50 or 60 miles an hour, it may be worthy of notice. It becomes important then to inquire what may be the greatest desirable speed to be maintained on railways for ordinary purposes. The wishes of the public will be limited only by considerations of economy and safety. The greater the speed the greater will be the cost; and it is generally believed that it will be difficult to maintain the present express speed on the great trunk railways. The chief impediments are,-