Profit in Contraries.
From this digression into matters of astronomy and of the human body and mind, let us return to the workshop and the engine-room. There is gain, as we have seen, when an inventor takes a familiar process, like planing, and reverses it, so that instead of the plane moving across a board, the board is moved beneath a planer. Not seldom, too, profit has followed upon adopting a plan just the contrary of a time-honored practice, as when a Frenchman pierced a needle with an eye near its point instead of away from its point, taking a step that did much to make the sewing-machine a possibility. Guns were loaded at the muzzle for ages, until one day a man of daring loaded them at the breech, to find that method preferable in every way. A bullet or ball might then be larger and closer in fit than before, have greater velocity and penetration, while truer in flight, especially if sped from a rifled gun. Anything left in the gun was in front of the new charge instead of behind it. In manufacture, the perishable parts of the gun, its vent and the adjacent steel, are now in a movable breech-piece where they may be replaced with little cost and trouble. Loading and firing may be much more rapid than with muzzle-loaders, while less space is required and the gunners are much less exposed than formerly. And ages before there was such a thing as a firearm, a vast stride in tilling the ground was taken simply by reversing an ancient practice. At first the soil was scratched by a stick drawn along its surface; when some primeval Edison gave the stick a forward instead of a backward thrust he created the 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.
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.
In an ordinary furnace the draft moves upward, obeying the impulse due to the lightness of its heated gases. This direction is reversed in down-draft furnaces which were originally devised by Lord Dundonald more than a century ago. In their modern types a fan blast forces the draft downward through the fuel, with the effect that the gases are so intensely heated as to be thoroughly burned. The grate-bars are of water-tube, connected to the boiler as part and parcel of its heating surface. In the Loomis gas-producer a like method is adopted: the fuel is charged through an open door in the top of the generator and the gas is exhausted from the bottom of the fire. Thus all tarry and volatile matter in bituminous coal or wood is converted into a fixed gas.
Thirty years ago one would have supposed the wheels of ordinary carts and carriages to be safe from change, to be among the heirlooms secure of transmission to posterity. Not so. Observe the wheel of a bicycle and note that instead of stout spokes upholding the hub, there are thin steel wires from which the hub is suspended. Thus strength is gained while the wheel is lightened and material economized. Wheels of like model are now used in many other vehicles where lightness is particularly desired. This plan of using spokes in tension instead of in compression is credited to Leonardo da Vinci who flourished four centuries ago.
Bicycle wheel suspended from axle by wires.