truck, in 1864 obtained a patent for improving Bissell's safety truck. Hudson contended that since the Bissell arrangement had a fixed pivot point it could traverse only one given radius accurately. He proposed to replace the fixed pivot with a radius bar (see fig. 5) one end of which was attached to the locomotive under the smoke-box and the other to rear of the truck frame, at the same point of attachment as in the Bissell plan. Thus, according to Hudson, the pivot point could move laterally so that the truck might more easily accommodate itself to a curve of any radius. He further claimed that a better distribution of weight was effected and that the use of the radius bar relieved the center bearing casting of much of the strain of propelling the truck.
[Illustration: FIGURE 8.--A 2-wheel Bissell truck installed on the Pennsylvania Railroad's No. 91. This engine originally an 0-8-0 Winans Camel built in February 1854, was rebuilt by John P. Laird in 1867, at which time the Bissell truc