Page:Popular Science Monthly Volume 88.djvu/672

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��Popular Science Monthly

��had just removed some of the shoring when earth began to drop rapidly away from one spot in the top of the tunnel. One of the men seized a bag of cement which is kept for such an emergency and attempted to block up the rapidly growing hole. Suddenly there was a report like a pistol shot. His startled comrades saw the man jerked up out of sight. Then they realized what hap- pened. The man had been blown away like a pea in a pea-shooter. One of the men managed to save himself by clinging to the shield. The other two victims were shot upwards to the surface of the river.

The instant that the work of rescue had been complet- ed, officials began the work of repair. It was found that the accident had been caused by a spot in the bed of the river which had been unable to withstand the air pressure of twenty- four pounds to the square inch that had been maintained in the tunnel. As a result the bottom of the river had blown out like a faulty automobile tire when overcharged with air.

Only once before in the history of tunneling has a workman been shot through the bed of a ri\'er and survived. Eleven years ago a "sand hog" was blown through the bed of the East River during the construction, of the present subway system. Although severely in- jured he survived the shock, and by a curious coincidence was working on the tunnel in which the recent accident occurred.

Militia Aero Corps

TWENTY-FOUR states are at pres- ent organizing aero corps to be in- cluded in their National Guards and Naval Militias.

���Spikes help a lineman to climb a wooden pole, but not a pole of steel. A shoe has been in- vented which enables a lineman to clamp him- self step by step on the steel pole

��Climbing Steel Poles with the Aid of Iron Shoes

IT was always an easy matter for a line- man to stick the points of his climbers into the sides of a wooden pole and reach the top with the agility of a squirrel. With the introduction of steel poles for high tension electrical lines, some other climbing help had to be found. A forged steel shoe has been invented, which is neatly strapped over the regular shoe.

The toe of the steel pole - climber curves upward. On its tip there are two steel projecting bearings or clamp- ing points, and these points tell the secret of the device. A square steel block, having four sharp corners is placed just beyond the toes of the steel shoe. When dull from use these corners may be substituted one for another.

This special block bears on the out- side of the steel pole, and a steel point situated at the end of the climber bears on the opposite side.

The climbers have a clamping action between the block and the point on the edge of the steel pole. This action is accomplished by the pressure of the lineman's weight on the end of the climber. Naturally his weight will come at the right point in climbing the pole. As he raises his foot for the next step, the lifted heel releases the grip of the climber. The steel climbers weigh about as much as the old style grippers used for the wooden poles.

��An Invisible Ink 'HEN the juice of an onion or lemon is substituted for ink, no visible effect is made on the paper until heated, when the writing will stand out very plainly.

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