“The framing for each engine of a pair is like a Porter bed standing on end with two posts forming what would be the lower part of the bed if it were lying down. There are therefore eight posts in the two pairs of engines, which form the second-story columns of the framing of the building, and the whole framing of the engines makes an integral part of the building construction, being rigidly connected with the beams of the fireproof flooring of all three floors. The building is four stories high. “The engines were started in 1867. They have been in continuous service ever since. Ten or twelve years ago I had an opportunity to measure the thickness of the crowns of the crank-pin boxes. They did not differ perceptibly from the thickness marked on the drawing from which they were made. Knowing the accuracy with which the work was made to correspond with the drawings (gun-shop work), I am confident that the wear of the box after twenty-six years of service had not amounted to five one-thousandths of an inch. All the parts give evidence of an almost indefinite durability. “All the work except that on the governors was done in the shops of the Colt company. The beds were cast in the foundry of one of the distinguished old engine-builders of Hartford, who felt it his duty to call on General Franklin, the general manager of the company, to warn him that if Richards were permitted to put a number of 75 horse-power engines running at 100 revolutions per minute, in the second story of a great building like the armory, disaster was certain. The building would be shaken so terribly. The fact is that any one standing on the third floor directly over the cranks would not know, from the movement of the floor or from sound, that the engines were running. The usual steam pressure carried when I was in the armory was from 50 to 60 pounds. The boilers then were large, of the drop-flue type. [Illustration: Card from Allen Engine in Colt’s Armory.] “Enclosed is a card taken in 1878 with the ‘pantographic’ indicator, for which a silver medal was awarded me at Paris in that year. The particular indicator with which this card was taken is in the Museum of the Conservatoire des Arts et Métiers. “Very sincerely yours, “C. B. RICHARDS.” This bold and successful piece of engineering would have made easy the introduction of these engines in New England. [Illustration: Professor CHARLES B. RICHARDS]