circa 1920s electro-magnetic Dynamo Demonstration Machine made by the Braun-Knecht-Heimann Co. of San Francisco: makers of educational science lab demonstration equipment -- works by pressing the wheel down with one lever, then rocking the top ratchet catch lever back and forth to turn the coil in 10-degree increments -- machine is app. 10 in. long --
-- moderate handling wear: has a 'supply' sticker on top / company label is a bit worn -- coil looks nice and magnets have pretty good charge-tested with a sensitive voltmeter and still seems to work --
-- *this is basically what this machine was designed to do:
"with this demonstration dynamo, each revolution of the crank lifts the ratchet,allowing a spring to rotate the coil through 10 degrees. [on this unit, it operates by pushing down the side lever, then rocking the top lever] As the coil moves through any 10-degree interval, an E.M.F. is induced which corresponds to the mean angular displacement of the coil from its original position."
ref: RA Millikan & J Mills, 'A Short University Course in Electricity, Sound and Light' (Boston, 1908) Central Scientific Co. Catalogue"* --
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