A COMPARISON—THE OLD AND THE NEW
Stephenson's locomotive and its tender, when loaded to full capacity with fuel and water, weighed seven and three-quarter tons. The locomotive itself was a trifle over seven feet long. In 1909 the Southern Pacific Railway purchased a Mallet Compound locomotive which, with its tender, weighs three hundred tons, or approximately forty times the weight of the little Rocket. This great locomotive is over sixty-seven feet long, or some nine times the length of the Rocket, and will haul more than twelve hundred tons back of the tender.
THE DEVELOPMENT OF THE LOCOMOTIVE.
The lower figure represents a longitudinal section of a modern French locomotive, for comparison with the sections of the famous engines of 1829. The weight of the "Rocket," with its four-wheel tender which carried 264 gallons of water and 450 pounds of coke was 4-1/4 tons. The French locomotive with its tender in working order, carrying 3300 gallons of water and five tons of coal, weighs 99 tons, and the length of the engine and tender is 56.3 feet.
The cylinders of the Rocket were eight inches in diameter, with a seventeen inch stroke; the high-pressure cylinders of this Mallet locomotive are twenty-six inches in diameter, and the low-pressure cylinders are forty inches. But curiously enough the driving wheels of the two engines show little discrepancy, those of the Rocket being fifty-six inches in diameter, as against fifty-seven for those of the larger engine. The total heating surface of the Rocket was one hundred and thirty-eight square feet, that of the new locomotive 6,393 square feet. To heat this great surface oil is used for fuel, so that the task for the fireman is lighter than on many locomotives less than one-half the size.
On this locomotive there are two sets of cylinders driving two sets of driving wheels on each side, making a total of sixteen drivers in all. From the size of these drivers it is evident that the engine is designed for strength rather than speed, although of course relatively high speed can be attained if desired. On the section of road over which it operates there is a maximum grade of one hundred and sixteen feet per mile, and it was for negotiating such grades with full loads that the locomotive was designed.
V
FROM CART TO AUTOMOBILE
THE use of the wheel as a means of reducing friction dates from prehistoric times. The introduction of this device must have marked a veritable revolution in transportation, but unfortunately we have no means of knowing in what age or country the innovation was effected. We only know that the Chinese have used wheelbarrows and carts from time immemorial, and that sundry very ancient pictures and sculptures of the Egyptians and Babylonians prove that these peoples were entirely familiar with wheeled vehicles.
The earliest form of wheel was doubtless a solid disk, and such a wheel is still in use in many places in the East; but the wheels of the Assyrian chariot were spoked after the modern fashion, and provided with rims of metal. The introduction of the wagon spring, however, was a comparatively modern innovation. The use of springs very considerably reduces the resistance, thus adding to the efficiency of wheeled vehicles; but the reduction is not very obvious unless the roads are tolerably good, nor is it probable that the ancient nations could readily have measured the effect even had the idea of springs suggested itself.
As regards good roads, these are, to be sure, no modern invention, since the Romans had carried the art of road-building to a very high degree of perfection. The integrity of the Roman Empire depended very largely upon the highways that linked all parts of its circumference with the Imperial centre; and in a perfectly literal sense all its roads led to Rome. The Roman roadbed was constructed of several layers of stone, and it was one of the most resistant and permanent structures ever devised. As late as the sixteenth century of our era there were no roads worthy of the name in England except the remains of those constructed many centuries before by the Roman occupants. It was not until well toward the close of the eighteenth century that Macadam and Telford devised methods of road-making whereby broken stone and gravel, pounded to form a smooth surface, gave the modern world roadbeds that were in any way comparable to those early ones of the Romans.
This development of road-building corresponded, naturally enough, with an advance in the art of carriage building, and the increased popularity of stage coaches. We are told that about 1650 the average rate of speed of the stage wagons in England was only four miles an hour; whereas the stage coaches moved over the improved roadbeds of the nineteenth century at an average speed of about eight miles an hour, which was sometimes increased to eleven miles. After about the year 1836, however, the stage coach was rapidly displaced by the steam railway, and the interest in roadbeds somewhat abated until brought again prominently to public attention by the users of bicycles and automobiles.