The point of interest in this incident was the fact that the gases had lost 125 degrees of heat in traversing a distance in flues and chimney of less than 20 feet. This seems difficult to believe, but they did. There was no leakage as the excellent draft clearly proved, nor any other way of accounting for the discrepancy. The length of the pyrometer tube exposed to the heated gases was the same in both positions. The heat had been lost by radiation through the brickwork. I have been waiting ever since for a chance to turn this knowledge to useful account, but it has not come yet. I will content myself with suggesting to somebody else the idea of facing the boiler setting, flues and chimney, not only outside but inside also after leaving the furnace, with white encaustic tiles, which will neither absorb nor radiate heat appreciably. This will pay in maintaining the temperature in a large degree to the top of the chimney, so increasing, perhaps doubling, the strength of the draft. An enormous amount of heat must be lost through the extended surface of the brick boiler setting. It is always observed that the hotter a boiler-room is kept the greater the efficiency of the boiler becomes. This is a slight indication of the great gain which might be effected by the plan I propose. Before this boiler trial we had lost Mr. Allen. He had conceived the idea of the pneumatic riveter and the high-speed air-compressor to furnish this riveter with power. In the latter he utilized the inertia of the reciprocating parts, including two pistons, the steam and the air piston. This he did with my cordial consent, and indeed there was nothing patentable about that feature anyway. Mr. Allen thus became the originator of the important system of pneumatic riveting, in its two methods, by percussion and by pressure. Mr. Allen sold out his stock in the engine company to Mr. Hope and Mr. Smith, and built a shop in Mott Haven for the manufacture of the riveters and compressors. He took the boiler in the fair in part payment, and sold it directly to a party who had erected a wood-working shop at some point on the Harlem River. The Croton water which had been fed to the boiler contained no lime, but some sediment. Mr. Allen had the boiler taken down and brought to our shop for inspection and cleaning. I determined to improve the opportunity to observe the effect of the circulation on the deposit of sediment, and the result of the examination proved most interesting. Each inclined tube had been provided at the end with a brass plug, by removing which it could be cleaned by the running out of the water which it contained. This had not yet been done.