Page:Popular Science Monthly Volume 89.djvu/701



ver much of northern Alaska and British Columbia the ground is forever solidly frozen for many feet beneath the surface. During the warm summer months, where the o\erl\ing mos> has been removed, the soil may thaw out for a few inches or feet, permitting placer mining to be carried on by hydraulic mining methods. For the most part this natural thawing is far too slow to prove practic- able in a region where the working season is only a few months in the year. The ingenuity of man, therefore, has devised a method to assist Nature in her work. Long, hollow ttibes, called "steam points," tapered at one end and enlarged at the other to withstand repeated blows and carrying a connection to a stt line, are driven in rows across the face of the grou Steam under pressure i forced through these pipes for several hours until the sec- tion is thoroughly thawed. Then the points are

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��n e a t h t h e ground in drifts, during the winter months, the gravel removed being piled in great dumps to await the summer season of abundant flowing water.

PATENT has been issued to William Heymann, of Washington, D. C, on a device which records on a graphophone drum whispered conversations, without the speaker being aware of the fact.

The receiver, which is of the usual detectaphone type, is to be worn beneath the shirtfront, and the electric battery and cylinder of the recording graphophone are to be hooked to the wearer's belt. Release a wound-up clock-spring and the needle of the graphophone traces the zig-zags produced by the sound waves.