By the 1870's, the _Pioneer_ was too light for the heavier cars then in use and by 1880 it had reached the end of its usefulness for regular service. After nearly thirty years on the road it had run 255,675 miles. Two new passenger locomotives were purchased in 1880 to handle the heavier trains. In 1881 the _Pioneer_ was dropped from the roster, but was used until about 1890 for work trains. After this time it was stored in a shed at Falling Spring, Pennsylvania, near the Chambersburg yards of the C.V.R.R. Mechanical Description of the _Pioneer_ [Illustration: Figure 11.--"PIONEER," ABOUT 1901, scene unknown. (_Photo courtesy of Thomas Norrell._)] After the early 1840's the single-axle locomotive, having one pair of driving wheels, was largely superseded by the 8-wheel engine. The desire to operate longer trains and the need for engines of greater traction to overcome the steep grades of American roads called for coupled driving wheels and machines of greater weight than the 4--2--0. After the introduction of the 4--4--0, the single-axle engine received little attention in this country except for light service or such special tasks as inspection or dummy engines. [Illustration: Figure 12.--THE "PIONEER" IN CARLISLE, PA., 1901. (_Photo courtesy of Thomas Norrell._)] There was, however, a renewed interest in "singles" in the early 1850's because of W. B. Adams' experiments with light passenger locomotives in England. In 1850 Adams built a light single-axle tank locomotive for the Eastern Counties Railway which proved very economical for light passenger traffic. It was such a success that considerable interest in light locomotives was generated in this country as well as in England. Nearly 100 single-axle locomotives were built in the United States between about 1845-1870. These engines were built by nearly every well-known maker, from Hinkley in Boston to the Vulcan Foundry in San Francisco. Danforth Cooke & Co. of Paterson built a standard pattern 4--2--4 used by many roads. One of these, the _C. P. Huntington_, survives to the present time. The following paragraphs describe the mechanical details of the _Pioneer_ as it appears on exhibition in the Smithsonian Institution's new Museum of History and Technology. BOILER