Page:Popular Science Monthly Volume 88.djvu/274

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��Popidar Science Morithly

��twelve feet. The loading platforms for the "extra elevated" express tracks are built over the existing local tracks, which are left unchanged. The length of the "hump" is determined by the grade of the present local tracks at that particular section, as the grade of the express

���This device permits accurate timing of the revolutions of a machine

tracks never exceeds three per cent. The new platforms are to be three hundred and fifty feet long.

It is expected that the cost of opera- tion of the express trains will be some- what decreased as the headway which they get on the incline will carry them some distance before power need be ap- plied. Trains will also be able to stop quickly and smoothly because of the up- ward incline as they enter the station.

Great credit is due the engineers en- gaged in the construction of the new tracks, for, with a few brief exceptions, traffic on the local tracks has not been interrupted.

A Revolution Timer and Stop Watch Ingeniously Combined

IT takes skill to time the number of revolutions a machine is making per minute, especially if it is running rapidly. One's attention is so divided between the watch and the revolution counter that it is difficult to start or stop the read- ing exactly on the second. In order to eliminate the human element and make

��the reading positive, a Chicago man has connected the revolution counter elec- trically with the watch.

Within the case of a stop watch is a tiny electro-magnet, which, when ener- gized, allows the second's hand on the watch to run ; but the instant the elec- tric current is broken and the magnet is no longer energized, the watch stops.

The electric current is furnished by a flash-light dry battery attached to the revolution counter, and the counter it- self is so constructed that the electrical circuit is completed the instant the counter starts to revolve and is broken the instant it stops.

The electrical mechanism does not in- terfere with the use of the watch, as a time piece or as a hand-operated stop- watch. The revolution counter may be used in the ordinary way if desired.

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��The Danger of Safety-Tin Boiler Plugs.

THE attention of the Bureau Standards of the Department Commerce has been called to a very seri- ous condition in the safety-tin boiler plugs used to warn engineers of dan- gerous boiler conditions. The plugs, which are made of fusible tin and which are supposed to melt easily when the temperature rises too high, were found on inspection to have become oxidized. Since the melting point of oxidized tin is about three thousand degrees Fahren- heit, one can readily see that the oxi- dized plugs, far from being a safety de- vice, actually increased the possibilities of danger from explosion. Lead and zinc impurities are found to be the prin- cipal causes of this oxidation in the tin ; and their elimination by strict inspection is urgently advised by the federal au- thorities.

Our Women Police

POLICEWOMEN are now employed in twenty-six cities. Chicago has twenty-one; Baltimore, Los Angeles and Seattle, five each; Pittsburgh, four; San Francisco, Portland, Oregon, and St. Paul, three each; and Dayton, Topeka and Minneapolis, two each. Fifteen other cities have one each. Their pay ranges from $625 a year in Dayton to $1,200 in San Francisco.

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