plow, and tillage began in earnest. In feeding coal to a fire, as in the case of a common grate, the one plan for centuries was to add the fuel from above. As gradually heated by the glowing mass beneath it, this fresh fuel sent forth comparatively cool gases which, to a considerable extent, passed into the chimney without being burnt. A mechanical stoker of the underfeed type forces fresh coal beneath the fuel already aglow; the result is that all the gases from the fresh coal pass through an incandescent bed which heats them highly, so that on emergence into the air-current they are thoroughly consumed. [Illustration: Link Belt Machinery Co.‘s Shop, Chicago, showing Sturtevant ventilating and heating apparatus.] In large machine shops a heating system is finding favor which equally departs from traditional methods. In a small workshop piping filled with steam or hot water serves well enough: in a lofty machine shop it serves badly, sending as it does warm currents of air toward the roof where warmth does only harm. The union of a fan with a system of steam coils introduces a vast improvement. Air warmed to any desired temperature is carried in ducts throughout the building, with outlets at the points most in need of heat. Instead of being allowed to take its way to the roof, the warmed air is forcibly directed to the floor which otherwise would be unduly cool. Because the air is in rapid motion the heating coils may not be more than one fourth as extensive as for a system of direct radiation. This plan has the further advantage of utilizing exhaust steam without producing undue back pressure on the pumps or engines, and yields results almost equal to those from live steam. See accompanying illustration. Lighting as well as heating may share the gain of changing an old method for its contrary. Many forms of reflectors, both in glass and metal, have been designed to scatter the beams of lamps, usually in a downward direction. An excellent plan directs the positive carbon of an arc-lamp to the ceiling instead of to the floor; from the ceiling, duly whitened, the rays descend more thoroughly and agreeably diffused than if reflected from mirrors or refracted by prisms, however ingeniously shaped and disposed. See illustration on page 75. In the days of small things in engineering, which ended only with Watt and his steam engine, when a kettle was to be heated the proper place for its fire was thought to be outside. But when big boilers came in, with urgent need that their contents be heated with all despatch, it was found gainful to put the fire inside. Stephenson owed no small part of the success of his locomotive, the “Rocket,” to its boiler being outside its flame. The most efficient modern boilers fully develop this principle.