That problem consisted, for one thing, in the practical use of a locomotive around curves of 400 feet radius. Cooper went back to New York, bought an engine with a single cylinder, rigged it on a car--not larger than a hand-car, geared it to the wheels of that car and solved the chief problem of the B. & O. His little engine--the _Tom Thumb_--was a primitive enough affair, but it pointed the way to these Baltimore merchants who were pinning their entire faith to their railroad project. * * * * * Two years after the beginning of the work, "brigades" of horse-cars were in regular service to Ellicott's Mills; by the first of December, 1831, trains--steam-drawn--ran through to Frederick, Md.; five months later, to a day, they had reached Point of Rocks on the Potomac, seventy miles from Baltimore. At Point of Rocks the road was halted for a long time. The power of the powerful Chesapeake & Ohio Canal, which had been great enough to keep State or national grants from struggling railroads, was raised to defend its claim to a monopoly of the Potomac Valley, by right of priority. This right was sustained in the courts, and the railroad held back two years, until it could buy a compromise. In 1835, a highly profitable branch was opened to Washington, while early in the following year, trains were running through to Harpers Ferry, at the mouth of the Shenandoah. During that same Summer of 1835, definite steps were taken toward the extension of the railroad to Pittsburgh, as well as Wheeling. But it was three years later before the struggling company was ready to make a surveying reconnaissance of these extensions of the road. All through that time actual construction work was slowly but quite surely progressing westward from Harpers Ferry, and on November 5, 1842, trains entered Cumberland, the one-time objective point of the enterprise. [Illustration: AN EARLY LOCOMOTIVE BUILT BY WILLIAM NORRIS FOR THE PHILADELPHIA & READING RAILROAD] [Illustration: THE HISTORIC "JOHN BULL" OF THE CAMDEN & AMBOY RAILROAD--AND ITS TRAIN] [Illustration: A HEAVY-GRADE TYPE OF LOCOMOTIVE BUILT FOR THE BALTIMORE & OHIO RAILROAD IN 1864. ITS FLARING STACK WAS TYPICAL OF THOSE YEARS] But beyond Cumberland the road gradually left the comfortable valley of the Potomac, and these early railroad builders found themselves confronted with new difficulties. To build a railroad across the range of the Appalachians, with the primitive methods and machinery of those days was no simple task. For nine years the construction work dragged. In 1851 the line had only been finished to Piedmont, twenty-nine miles west of Cumberland, and its builders were well-nigh discouraged. Let us quote from the ancient history of the B. & O., from which we derive these facts, in an exact paragraph: