818 



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. 



