INVENTION OF THE LINK.
There is no doubt but the link was first applied to a steam engine by William T. James of New York, a most ingenious mechanic, who also invented the double eccentrics. James experimented a great deal about the period from 1830 to 1840, with steam carriages for common roads; and it was in this connection that he invented the link. His work having proved a commercial failure, the improvements on the valve-motion were not recognized at the time; although the probability is, that Long, who started the Norris Locomotive Works of Philadelphia, and brought out the double eccentrics upon the locomotives built there, was indebted to James for the idea of a separate eccentric for each direction of engine movement.
The credit of inventing the ordinary shifting link is due to William Howe of Newcastle, England. This inventor was a pattern-maker in the works of Robert Stephenson & Co., and he invented the link in 1842 in practically its present form. The idea of Howe was to get out an improved reversing motion; and he made a pencil-sketch of the link, to explain his views to his employers. The superintendent of the works was favorably disposed to the invention, and ordered Howe to make a pattern of the motion, which was done; and this was submitted to Stephenson, who approved of the link, and directed that one should be tried on a locomotive. Although Stephenson gave Howe the means of applying his invention, he does not seem to have perceived its actual value, for the link was not patented; and Stephenson never failed to patent any device which he thought worth protecting.
The link-motion was applied to a locomotive constructed for the Midland Railway Company, and proved a success from the day it was put on. Seeing how satisfactorily the invention worked, Robert Stephenson paid Howe twenty guineas (one hundred and five dollars) for the device, and adopted the link as the valve-gear for his locomotives. This is how the shifting link comes to be called the “Stephenson link,” and the credit for this invention was not extravagantly paid for.
The capability which the link possesses of varying the steam admission and release, did not appear to be understood by the inventor; nor was the mechanical world aware, for some time after the link was brought into use, that it could be employed to adjust the inequality of steam distribution, due to the angularity of the connecting rod.