[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driving wheels, was largely superseded by the 8-wheel engine.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.