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[[preprinted]]
May, 1911    AVIATION    19

revolutions per minute of the motor. The small magneto, which generates the current to actuate the galvanometer mounted on the aeroplane, is driven from the engine by a rubber belt or a spring-steel belt, indicating the revolutions per minute from zero to 5000 by the hand on the calibrated dial of the galvanometer, and the current is led to the galvanometer through insulated, flexible copper wire of low resistance.

[[image: drawing of an early aero tachometer. Drawing by A. DUBRAY.]]
[[caption]] Tachometer [[/caption]]

Indicator Showing Angle of Ascent and Descent

This is an indicator to show the angle of ascent and descent made by the chord of the wings in relation to the horizontal. The instrument is placed on a mounting attached to the frame of the aeroplane and it is so regulated that the colored liquid in the glass tube stands at zero when the chord of the planes in horizontal. Then when the aeroplane is in flight the angle of the chord of the planes in relation to the horizontal will be shown by the position of the liquid before the graduated scale in degrees of positive angle or negative; according as the liquid is below or above 0.

[[image: drawing of Ascent/Descent Indicator. Drawing by A. DUBRAY.]]
[[caption]] Indicator Showing Angle of Ascent and Descent [[/caption]]

Compass for Dirigibles and Aeroplanes

This special compass is very easy to read, having a needle pointing to the geographic north, and a black star to the south, while on the card a red star is adjustably mounted. The crystal has circular graduations in degrees from zero to 180. The graduations start from 0 at the rear, marked A.R., and numerals increase on both sides from zero to the 180 degrees division. The front, marked A.V., and the angle at which the dirigible or aeroplane moves in relation to the geographic

[[image: drawing of a compass. Drawing by A. DUBRAY.]]
[[caption]] Compass for Dirigibles and Aeroplanes [[/caption]]
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