Page:Popular Science Monthly Volume 88.djvu/769

 Popular Science Monthly

��A Scientifically Designed Train- Announcing Megaphone

A GIGANTIC megaphone for an- nouncing the arrival and departure of trains at the Pennsylvania Railroad's terminal in Washington, D. C., has been developed to such a degree of success that sounds emitted by it reach clearly to every corner of the huge station, despite the fact that the announcer is not required to raise his voice much higher than an ordinary conversational tone. The megaphone, which is mount- ed on a high wooden platform, is interesting, not only because of its gigantic proportions — for two men could crawl inside and hide comfortably — but also because it is the culmination, of a great many painstaking experiments.

A. M. Keppel, who is the designer, has tried out in the huge horn almost every applied principle of acoustics. A dozen horns of various sizes, shapes and groupings have been installed, improved and discarded. The present megaphone is considered to be the most satisfactory of all. Probably the most important discovery in connection with all of the devices tried was that a flat horn carries sound with fuller volume and less distortion than a round horn of the same general proportions. Accordingly, a huge flat megaphone was built and a number of smaller horns were secured

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within it, all being controlled by a single mouthpiece. As it now stands the horn contains no inner megaphones. Long

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which can handle one cubic yard of crushed rock in a

minute and a quarter

��A megaphone which was built to carry sound without the waste of a single vibration

iron wires have been attached, extending from near the mouthpiece to beyond the end of the horn. Their purpose is to prevent echoing, and to purify and clarify the sound. The giant mega- phone measures ten feet four inches across the large opening and eight feet in length.

Wagon-Loader Re- sembles Gold -Dredge A WAGON-LOAD- ING machine has been brought out which in appearance and opera- tion is a repHca in minia- ture of the huge dredges used in Cahfornia and Alaska for mining sur- face-gold. To a chain passing around two pul- leys, one at either end of a steel frame, small steel scoops or buckets are attached at regular in- tervals. An electric mo- tor supplies the power.

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