Page:Popular Science Monthly Volume 91.djvu/129

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Popular Science Monthly








��The traps are spread from the coast of France clear across the English channel

would still be so were the grand fleet in the Orkneys to be destroyed.

When United States Naval officers were consulted concerning the use of these nets, and the possibility of such a method they unanimously agreed that it was possible, although they knew nothing about it. They said that nets were certainly being used and that very probably the minor difficulties in their way had been solved.

��The Latest Salvaging Device for Metals — An Electromagnet

A LIGHTER acci- dentally turned over at sea, spilling several thousand cases of shells. A diver was put on the job, but owing to the ice and extremely cold water, he was able to work only a few hours at a time. At the end of a day less than one hun- dred cases had been raised.

An electromagnet was installed and dropped to the river bottom. On the first trip it recovered four cases. This was repeated again and again, until at the end of the day over two hundred boxes had been brought to the surface.

A large number of cases were broken, so that the shells fell out and sank deep in the mud. This magnet was found powerful enough to draw both shells and cases out of the mud.

����The electromagnet diver bring- ing to the surface cases of shells some of which were buried in mud

��The English fleet, anchored in the Orkney Islands, is completely protected by the nets

In fact when a shell is left at a distance of about twelve inches from the magnet and the current turned on, the shell, weighing about 255 pounds, jumps to the magnet.

The outfit consists of a gasoline-driven generator, control apparatus for the mag- net, and the magnet, which weighs about 9,000 pounds, and requires from eighty to ninety amperes at 240 volts direct current to energize it.

The magnet was attached to the cable, and by means of a swinging boom could cover a large area without having to move the lighter on which the apparatus was located.

In operation, the magnet was lowered to the bottom of the river, a depth of between thirty and forty feet; then the current was turned on and the magnet lifted. Then the boom swung the magnet over to the deck, the current was switched off, and the cases of shells were dropped.

This type of magnet (designed for handling scrap iron and steel) though never intended to operate under water, is quickly attached and in this particular case was operated with marked success for ten consecutive days with no special at- tention or repairs except perfunctory tightening of the bolts and filling the main feed cables with tar. The cases of shells were recovered with compara- tive ease. The method will probably be used for other salvaging purposes.

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