Page:Popular Science Monthly Volume 88.djvu/846

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��Popular Science Monthly

���A bridge, two miles in length and twenty feet wide, is stretched across Pen d'Oreille Lake, for the use of farmers who sell their produce in Sandport, Idaho

��The Longest Wagon-Bridge in the World

IN the accompanying photograph is shown a bridge two miles long, twen- ty feet wide and twenty-five feet high. The tower in the center is the draw- bridge through which vessels pass. By turning a heavy iron wheel the weights at the top of the tower are lowered to throw the bridge open.

This bridge is on the Pen d'Oreille Lake, and was built for the benefit of the farmers across the lake, as they had no other way of getting across water to Sandpoint, Idaho, to sell their produce and do their marketingf.

��T

��Healing Magic of the Electric Arc

HE most intense heat produced by

��man is that of the electric arc, and the possibilities of its application in vari- ous branches of American industry have

���only begun to be realized. Like many other useful scientific agents, the elec- tric arc has been adopted by the burglar. There is no safe known that will not yield to the electric carbon applied by the skilled "safe-cracker."

Aside from lighting, the most useful purpose to which the electric arc has been put is in the mending of broken or cracked castings and metal parts of all kinds. A broken shaft, for instance, can be resurrected from the junk heap if a skilled workman, with adequate arc ap- paratus, is given a chance at it. More- over, a broken metal piece repaired by the electric arc is as serviceable as when new. In fact, strain tests made upon repaired castings often result in break- age at a different point than where the repair was made.

The accompanying photograph shows a workman engaged in arc-welding. Due to the intense heat at the point at which the carbon pours its electrical fire upon the metal, the operators usually wear helmets, not unlike the gas helmets of the present war. They at least hold be- tween their eyes and the arc a thick plate of cobalt glass. The amount of protec- tion required depends upon the strength of the current fed to the arc.

��Broken or cracked castings can be quickly mended by means of an electric arc

��Watch Your Oil for Gold Teeth

WHILE overhauling an old, two- cylinder car, E. E. Booth, of Po- mona, Cal., found in the crank case a sizable piece of refined gold which had apparently been once the crown of some- body's tooth. Its presence in the oil and other residue has not been explained.

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