English: An elevation drawing of the 4-2-0 locomotive Experiment, designed by engineer John B. Jervis and built in 1832 for the Mohawk and Hudson Railroad. Experiment was the first locomotive to have a pivoting leading four-wheel truck (bogie) for guidance, an invention that soon entered wide use on locomotives in the United States and other countries. This drawing shows Experiment as first built, with a long shallow firebox that was intended to burn anthracite, a hard coal which burns slowly. As it turned out, the locomotive had trouble producing sufficient steam with this firebox even when wood fuel was used. It was rebuilt in 1833 with a shorter and deeper wood-burning firebox; renamed Brother Jonathan, it was much more successful in this form.