Page:Popular Science Monthly Volume 90.djvu/751

Rh An Electric Semaphore Signal for the Automobile

IKE an ordinary semaphore, the elec- trically - lighted automobile signal shown in the illustration drops to a hori- zontal position to indicate the direction the car will take in turning. As the arm drops, it is lighted automatically.

The entire signal consists of two semaphores attached to the sides of the windshield and operated by means of wires tightly wound around small drums on the dash.

Small knobs on the drums allow the driver to drop either light at will by turning either knob and re- leasing the wires. Red and green lights are generally used for such signals.

Stock Power Sand Screens for Small Jobs

ASILY movable from place to place on a contracting job, the power-driven sand and gravel screen shown in the accom- panying illustration is designed for small jobs where the cost of erecting a permanent screen would be pro- hibitive but where the old hand methods would prove too slow and too costly.

The screen consists of an open cylinder carried on a shaft at its center and supported on a metal framework with small wheels on the bottom. The cylinder is made in several ring sections over which are bolted semi- circular screens covered with wire netting of close and open weave.

The sand is fed into one end of the screen by means of a hopper and chute.

As the screen revolves, the sand passes through the meshes of the dif- ferent sections, the finest sand dropping through to the ground first and the large stones passing through clear out to the end. The varying grades of sand are sepa- rated on the ground by means of small boards as shown in the picture.

Another un- usual feature of the screen shown is a me- chanical screen cleaner work- ing on the hammer or im- pulse principle. This cleaner consists of an inverted U-shaped frame bolted to the sides of the screen framework over the section having the finest screen. A hori- zontal arm pivoted to one of the vertical arms of the U-frame ter- minates in a small metal roller at its free inner end which contacts by gravity with a narrow steel ring around the screen, imparting ham- mer-like blows to the ring and screen suffi- cient to jar free any particles clogging it.

"The use of wire screens instead of perforated metal is a new departure in small capacity screens. It has been found that the rough- ness of the wire netting offers sufficient resistance to the sliding mass to hold it until the part that should sift through has fallen out. thus insuring uniform grad- ing of the material.

The field of the screen iis [sic] not limited to sand alone It may be used for coal coal screenings and the like