With the improvement of brakes and more reliable means of stopping trains upon steep grades, came a farther development of the above device, which was first applied on the Denver and Rio Grande Railroad in Colorado, and has since been applied on a grand scale on the Saint Gothard road, the Black Forest railways of Germany, and the Semmering line in the Tyrol. This device is to connect the two lines of the zigzag by a curve at the point where they come together, so that the train, instead of going alternately backward and forward, now runs continuously on. It becomes possible for the line to return above itself in spiral form, sometimes crossing over the lower level by a tunnel, and sometimes by a bridge. A notable instance of this kind of location is seen on the Tehachapi Pass of the Southern Pacific, where the line ascends 2,674 feet in 25 miles, with eleven tunnels, and a spiral 3,800 feet long. [Illustration: Plan of Big Loop.] The "Big Loop," as it is called, on the Georgetown branch of the Union Pacific, in Colorado, between Georgetown and a mining camp called Silver Plume, has been chosen to illustrate this point. The direct distance up the valley is 1¼ miles and the elevation 600 feet, requiring a gradient of 480 feet per mile. But by curving the line around in a spiral, the length of the line is increased to 4 miles and the gradient reduced to 150 feet per mile. Zigzags were used first for foot-paths, then for common roads, lastly for railways. Their natural sequence, spirals, was a railway device entirely, and confirms the saying of one of our engineers: "Where a mule can go, I can make a locomotive go." This may be called the poetry of engineering, as it requires both imagination to conceive and skill to execute. * * * * * [Illustration: Profile of the Same.] There is one thing more which distinguishes the American railway from its English parent, and that is the almost uniform practice of getting the road open for traffic in the cheapest manner and in the least possible time, and then completing it and enlarging its capacity out of its surplus earnings, and from the credit which these earnings give it. [Illustration: Big Loop, Georgetown Branch of the Union Pacific, Colorado.] The Pennsylvania Railroad between Philadelphia and Harrisburg is a notable example of this. Within the past few years it has been rebuilt on a grand scale, and in many places relocated, and miles of sharp curves and heavy gradients, originally put in to save expense, have been taken out. This system has been followed everywhere, except on a few branch lines, and upon one monumental example of failure--the West Shore Railroad, of New York. The projectors of that line attempted in three years to build a double-track railroad up to the standard of the Pennsylvania road, which had been forty years in reaching its present excellence. Their money gave out, and they came to grief. II.