Page:Popular Science Monthly Volume 90.djvu/756

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��Popular Science Monthly

��the base, and two thousand and one hun- dred feet long on the crest. The total cost of the reservoir was about $5,000,000.

A large water power plant has been con- structed below the dam, to convert the energy of the water as it is released from the reservoir into electric power. As this plant will in a few hours use up all the water available for an entire day, a bal- ancing or equalizing reservoir has been built a short distance below the power house to receive the water discharged from the turbines and deliver it uniformly throughout the twenty-four hours to the stream below.

The other ten reservoirs on the Ruhr Basin were built between 1894 and 1912, and vary in ca- pacity from six- teen to six hun- dred and sixty million cubic feet. The dams are all of rubble mason- ry, arched up- stream like the Mohne Dam, and vary in height from sixty-four to one hundred and thirty-three feet.

A project much like the original Ruhr Association has re- cently been proposed on the Naugatuck River in Connecticut. Twenty-five cor- porations with manufacturing plants along this stream have agreed to cooperate in the construction of three storage reser- voirs with a combined capacity of 1,736,- 000,000 cubic feet at a cost of several million dollars. The purpose of these re- servoirs is to increase the low-water flow in order to overcome the present shortage of water for industrial purposes.

The Beaver River Valley in western Penn- sylvania presents ideal conditions for the formation of a water users' association modeled after that on the Ruhr River. The low-water flow is entirely inadequate to supply the thickly populated manufac- turing district bordering the river. The State Water Supply Commission in 1912 showed that a storage reservoir impound- ing about eight billion cubic feet could be built at a cost of about $1,600,000.

���Underwood and Underwood, N

��Looking into the little inclined mirror in front of him the soldier sees the image of the rifle sights and the view beyond, thrown from the mirror above

��Combining the Periscope with the Military Rifle

PERISCOPE, an instrument for seeing over intervening objects" — so the dic- tionary says.

About three hundred ingenious and hope- ful inventors have gone to the Patent Office and then to various military head- quarters with different designs of periscope- sighted rifles since the war began. Most of these schemes were more ingenious than practical ; few of them had enough original- ity to be worth much.

The rifle attachment here illustrated is one of the most workmanlike and practical applica- tions of the idea of so rigging a rifle with a pair of mirrors that one can "lay" it ac- curately on the other fellow while remaining snugly below the trench level and exposing only the rifle.

The primary principle of all such arrange- ments is that if you place a mirror on a line with the sights of the rifle and arrange it at the proper angle, and have another mirror a sufficient distance be- low, the second mirror picks up from the first one above the image of the rifle sights and reveals the spot where the enemy is supposed to be.

Gazing at the little incHned mirror in front of him, the soldier sees the reflection of the rifle sights and the view beyond the rifle, sent down by the mirror placed at the top end of the tube. The rifle is aligned and held against the kick of firing by the detachable piece fastened to the rifle stock, while it is fired in the normal way. The soldier is therefore able to take accurate aim without exposing himself above the trench parapet. Tommy Atkins aided by Mother Necessity, evolved a dozen difl^er- ent modifications of the periscope idea, from two bits of pocket mirror, and some sticks. Try it yourself with a piece of cut-out stove pipe and two mirrors placed at proper angles at top and bottom.

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