“Long Branch, N. J., Aug. 7th, 1872.
“Mr. Chas. T. Porter:
“My dear Sir: Since I had the pleasure of reading the paper which you read before the Polytechnic Club last winter, I have regarded your demonstration as not less original than subversive. It is, for the first time I believe, apprehended and asserted, not merely that the vis inertia of the reciprocating masses is not primarily an adverse element in the economy of the crank-engine, but that a certain amount of weight in the piston and its connections, and in high-speed engines a very considerable amount, is an absolute theoretical necessity.
“As this will be deemed rank heresy by folks who have been making skeleton pistons of wrought iron, it is well perhaps that you are entrenched at the outset behind the experimentum crucis of loose brasses. “Very truly yours,
“Joseph Nason.”
The following [figures] represent an elegant invention of Mr. Edwin F. Williams, which exhibits graphically the acceleration and retardation of the reciprocating parts of an engine.
In these views, A is the cross-head in its mid-position; B is the lath by which the paper drum of an indicator is actuated through the cord n. The lower end of this lath is fixed in its position on the cross-head by the stud j, on which it turns freely. y is the end of a vibrating arm, which permits the point of suspension of the lath B to fall below the position shown, as required in the motion of the cross-head on account of the lower end of the lath being so fixed. d is a cylindrical box, partly open, which is secured on the side of the cross-head, in a position parallel with motion, by the arm P. The end of this arm is on the stud j, inside the lath B. It is prevented from turning on this stud by the set-screw K, and its fixed position is further assured by the stud r.
In the box d is the cylindrical weight h, running freely on rollers, not shown, and bored to receive a spring e, of known strength. This spring is secured in two heads, one of which is screwed into the box and the other into the weight. The force required to move the weight h is thus applied to it through the spring.
The operation of this instrument is as follows: The cross-head being at its mid-stroke, as represented, has acquired its full velocity. At this point no force is being exerted, either to impart or to arrest its motion. The same is the case with the free weight h. No pressure is here being exerted, either to compress or to elongate the spring e.
Joseph Nason