Page:Popular Science Monthly Volume 88.djvu/401

 Popular Science Monthly

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���Railroad Gate Warns and Stops Reckless Motorists

ANEW safely gate has been put in use on crossings to warn motorists when a train approaches and stop them if they do not heed the warning. Elec- trical contacts are fastened to the rail- road track a few hundred feet from the road crossing. Wiien a train rolls over them, current is sent to an iron box on a pole at the side of the road. A bell clangs loudly — this is the warning — and at the same time, a long steel arm swings out over the road. At equal dis- tances along the arm "tell-tales" are hung. These are steel wires wound in a spiral, usually about eight feet long. A

��When the train approaches, a bell rings, a signal light flashes, and the arm of the pole drops down, thus lowering a number of heavy spiral wire tell-tales which should stop the most reckless motorist

motorist, no matter how reckless, will think twice before he risks these tell-tales. At night, in case an auto- mobile driver should misunderstand the bell, a bright ruby light shines down the road, while a white light, fixed at right angles to the other, illuminates the safety arm and dang- ling tell-tales.

When Will This Reservoir Be Emptied?

SUPPOSE we have a reservoir a mile square and one mile deep and we as- sume that the water in it does not evapo- rate and is not added to by rain or other causes. Again, let us suppose that there is an outlet in the bottom of the reser- voir through which the water escapes at the rate of one hundred gallons per second (more water than most families use in a day). When will the reservoir be empty?

A few minutes work with pencil and paper will suffice to show that you would never see the bottom of this artificial laK-e — no, nor your great-grandchildren. In fact it would take some three hun- dred and fifty years to empty the tank.

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