The three plates were necessary to the production of one. They have also a permanent use. They are indispensable to the preservation of the true plane, which it has cost so much patient labor to produce. The date of their completion is stamped on their edges. Then plates 1 and 2 are put away in the store-room, their surfaces carefully protected from rust or injury, which last is best avoided by inverting one on the other, and No. 3 is put into use. A prominent use is for the production of smaller plates or straight-edges adapted to special purposes. After a while, perhaps in a little while, this plate loses its truth by unequal wear. Indeed, speaking with absolute truth, it may be said that the first time this plate is used it is ruined. But by taking pains to use different parts of its surface as equally as possible, it may be kept in fair condition for some time. It can at any time be restored to its original condition by scraping it to No. 2, taking the same pains to turn it one quarter way around at every rub. In the course of time No. 2 will itself become worn unequally, when its truth can be restored by rubbing it on No. 1. Finally the three plates can all be restored to their original condition by rubbing them together interchangeably as at first. Thus the true plane can be absolutely perpetuated. The importance of this work can only be realized when we consider that the true plane affords the only means by which true cylindrical work also can be either produced or verified. It is thus seen to be fundamental to all mechanical truth. CHAPTER XXII Efforts to Resume the Manufacture. I Exhibit the Engine to Mr. Holley. Contract with Mr. Phillips. Sale of Engine to Mr. Peters. In the years ’74 and ’75 I was filled with eagerness to get the engine on its legs again, and tried a number of schemes in vain. One morning I read in the paper that Alexander L. Holley had just returned from Europe, where he had been making a tour of the steel-making establishments, studying both the Bessemer and the open hearth or Siemens-Martin processes, on a scheme of interchanging improvements in manufacture between American and foreign licensees under both these systems. It occurred to me that Mr. Holley might be the very man I wanted. If he could be got to recommend the engine to the steel-makers, they might take it up for their own use. I had not applied the engine in rolling-mill work, but felt sure that it would prove especially adapted to that service. So I called on Mr. Holley at his home in Brooklyn. I had never before met him, but I found that he knew something about the engine from its exhibition in Paris, and from his brother-in-law, Frederick J. Slade, then an officer of the New Jersey Steel Company, and who was one of the engine’s warm admirers. I have already mentioned Mr. Slade and the help he gave me while in Paris in solving the problem of piston acceleration. [Illustration: ALEXANDER LYMAN HOLLEY]