The subject of an indicator directly presented itself. Mr. Allen invited Mr. Richards and myself to his engine-room, and took diagrams for us with a McNaught indicator. This was the first indicator that either of us had ever seen. Indicators were then but little known in this country. The Novelty Iron Works made a very few McNaught indicators, almost the only users of which were the Navy Department and a few men like Mr. Ericsson, Mr. Stevens, Mr. Sickels, and Mr. Corliss. I told Mr. Richards that we must have a high-speed indicator and he was just the man to get it up for us. He went to work at it, but soon became quite discouraged. He twice gave it up. He could not see his way. I told him I was not able to make any suggestion, but the indicator we must have, and he had to produce it. After some months he handed me a drawing of an indicator which has never been changed, except in a few details. This important invention, which has made high-speed engineering possible, came from the hands of Mr. Richards quite complete. Its main features, as is well known, are a short piston motion against a short, stiff spring; light multiplying levers, with a Watt parallel motion, giving to the pencil very nearly a straight line of movement; and a free rotative motion of the pencil connections around the axis of the piston, which itself is capable of only the slight rotation caused by the compression or elongation of the spring. Elegant improvements have since been made, adapting the indicator to still higher engine speeds; but these have consisted only in advancing further on the lines struck out by Mr. Richards. In fact, this was all that could be done--giving to the piston a little less motion, lightening still further the pencil movement, and making the vertical line drawn by the pencil more nearly a straight line. [Illustration: DIAGRAM TAKEN SEPTEMBER 13, 1861, FROM THE FIRST ALLEN ENGINE BY THE FIRST RICHARDS INDICATOR. ENGINE, 6 INCHES BY 15 INCHES, MAKING 160 REVOLUTIONS PER MINUTE. THIS CARD WAS RUN OVER TWENTY TIMES.] I took Mr. Richards’ drawing to the Novelty Iron Works and had an indicator ready for use when the engine was completed. The engine was made by the firm of McLaren & Anderson, on Horatio Street, New York, for their own use. It was set up by the side of their throttle-valve engine, and was substituted for it to drive their machinery and that of a kindling-wood yard adjoining for which they furnished the power. It ran perfectly from the start, and saved fully one half of the fuel. In throttle-valve engines in those days the ports and pipes were generally so small that only a part of the boiler pressure was realized in the cylinder, and that part it was hard to get out, and nobody knew what either this pressure or the back pressure was. I have a diagram taken from that engine, which is here reproduced.