Popular Science Monthly 



373 



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. 



