Engineering reminiscences contributed to "Power" and "American machinist"

by Charles T. Porter

This exhibited at once the equalizing action of the reciprocating parts in a cut-off engine, absorbing the excessive force of the steam at the commencement and imparting it to the crank at the end of the stroke. I feel myself more indebted to Mr. Slade than to any one else, and would here record the tribute of my grateful acknowledgment.

On January 30, 1868, I had the honor of reading a paper on the Allen engine before the Institution of Mechanical Engineers. The discussion of the paper was postponed until the next meeting, April 30, and the paper was ordered meantime to be printed and sent to the members. The result was that on the latter date we had a very interesting discussion. I may mention two things which occurred at the first meeting, but do not appear in the report of the transactions. When the secretary reached the statement that the acceleration of the piston was greatest at the commencement of the stroke, the president of the meeting, Sampson Lloyd, Esq., one of the vice-presidents of the Institution, stopped the reading and said to me, “You do not mean, Mr. Porter, that this is on the commencement of the stroke, but at a point near its commencement.” I was obliged to answer him that I intended to say that precisely on the dead center, at the point where motion in one direction had ceased and that in the opposite direction had not yet commenced, at that precise point the stress on the crank was at its maximum, the crank having brought the reciprocating parts to rest, and then by a continuance of the same effort putting them in motion in the reverse direction.

Frederick J. Slade

After the reading was concluded, Mr. E. A. Cowper took the floor, and stated that I was entirely mistaken in my explanation of this action, that this had been investigated by a gentleman whose name he gave but which I have forgotten, and who had demonstrated that this retarding and accelerating action was represented by a curve, which approximately he drew on the blackboard, but which he excused himself from demonstrating there, as it would require the use of the calculus and would take considerable time. For this reason the discussion was postponed. At the next meeting Mr. Cowper did not present this demonstration, and long afterwards he wrote a letter to the editors of Engineering, stating that on full investigation he had found the retardation and acceleration of the piston to be represented by triangles and not by a curve. At the discussion of the paper my view was supported by all the speakers who addressed themselves to this point, except Mr. Cowper. An especially careful and valuable exposition of the action of the reciprocating parts was given Mr. Edwin Reynolds, then of the Don Steel Works, Sheffield.

Zerah Colburn, the editor of Engineering, had always taken a warm interest in my engine, and in the winter following the Paris Exposition he invited me to furnish him the drawings and material for its description in his paper. This I did, and from these he prepared a series of articles written in his usual clear and trenchant style. These will be found in Volume V of Engineering, the cuts following page 92, and the articles on pages 119, 143, 158, 184, and 200.

Mr. Colburn’s articles in Engineering are so interesting in themselves that I think I need make no apology for quoting from them his remarks on this subject of the inertia of the reciprocating parts, and those in which is depicted the revolutionary nature of the high-speed engine, as viewed at that time.

After a prelude, with most of which the reader is already acquainted, Mr. Colburn says:

“When a steam-engine is brought from abroad to the very spot where the steam-engine originated, and where it has received, so far at least as numbers are concerned, its greatest development, and is claimed to be superior to those produced here, and to be able to run advantageously at a speed hitherto deemed impracticable, its promoters must not expect to have much attention paid to its claims until such attention has been actually compelled, and then they must be prepared for an ordeal of severest criticism....

“In employing a high grade of expansion, especially with the considerable pressure of steam now usually carried in stationary boilers, two serious practical difficulties are met with. The first arises from the injurious effect of the sudden application of so great a force on the centers, which the beam-engine, indeed, cannot be made to endure, and the second is found in the extreme difference between the pressures at the opposite ends of the stroke, which is such that the crank, instead of being acted upon by a tolerably uniform force, is rotated by a succession of violent punches, and these applied when it is in its most unfavorable position....