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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, wliich, 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 tliat 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. 



of 



of 



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. 



