The British journal _Engineering_, in an article otherwise friendly to the inventor, expressed some skepticism as to the real merit of Hudson's invention.[15]
If Mr. Hudson's truck, ... be examined, it will be seen that the radius link serves no other purpose than that of carrying the truck along with the engine, and this could obviously be equally done by the pivot or central pin of the truck itself.
It is probable that few builders other than Rogers made use of the Hudson radial link.[16] One of these was John Headden, whose _General Darcy_, shown in figure 6, was fitted with the Hudson truck.
Thus, by 1860 there had been perfected and adopted a successful 4-wheel safety truck for 4-4-0's and 4-6-0's used in general mixed and passenger service. But as the decade advanced, the need grew for heavy freight engines that could be safely run at speed. Without a pilot truck, the leading driving axle of the freight engine was generally overloaded. While the application of a 4-wheel truck reduced this front-end overload and permitted faster running it materially reduced the traction of the drivers by bearing too great a portion of the total weight. This loss of traction was of course highly undesirable and generally disqualified the use of 4-wheel trucks for freight engines. What was needed was a truck which would guide the 0-6-0's and 0-8-0's around curves and yet leave the greater portion of the weight on the drivers. The 2-wheel, or pony, truck met these requirements.[17]
[Illustration: FIGURE 9.--Running gear and truck designed by John L. Whetstone, as shown in the drawing for U.S. patent 27850, issued April 10, 1860.]
Levi Bissell produced the basic patent for such a truck in 1857. Zerah Colburn in September of that year had suggested to Bissell that he develop a 2-wheel truck. Such a device, he believed, would be well received in Britain.[18] He was quite correct, as will shortly be seen.
In nearly every respect Bissell's 2-wheel truck (see fig. 7) followed the idea of the original patent for the 4-wheel truck, which he claimed as the basis for the present invention. The pintle was located behind the truck axle, near the front driving-wheel axle, and the weight was carried by incline planes that also served as the centering device.