The Figure of the Earth

   Quote, without comment, from the Illustrated Descriptive Catalogue of Optical, Mathematical  and Philosophical Instruments published in 1856 by Benjamin Pike, Jr. of New York:

   "All globular bodies, whose parts can yield, and which do not turn on their axes, must be perfect spheres... But all such globes which do turn on their axes will be oblate spheroids, that is, their surfaces will be higher, or further from the centre, in the equatorial than in the polar regions. For, as the equatorial parts move quickest,  they must have the greatest centrifugal force; and will therefore recede furthest from the axis of motion. Thus if two circular hoops..., made thin and flexible, and crossing one another at right angles, be turned round their axis, ... and the axis be made loose in the pole or intersection [at the top], the middle parts ... will swell out, so that the whole will appear of an oval figure, the equatorial diameter being considerably longer than the polar."

   The figure of the earth demonstrator at the right is in regular use at Kenyon College in Gambier, Ohio.
 
                               St. Mary's College                                                                    Kenyon College

   The two instruments below were made by James W. Queen of Philadelphia, and are listed, with a complete set of accessories, at $11.00 in the 1881 catalogue. The device is 15½ inches high and 17 inches wide. The figure of the earth demonstration was made of spring brass.
 
                           Smithsonian Institution                                                                   Miami University
 
   This figure of the earth demonstrator was made by Ritchie of Boston. In his 1860 catalogue, he wrote: "Whirling Machine; illustrating central and centrifugal forces, the flattening of the poles of the planets, the revolution of bodies on their shortest diameter; mahogany from, 20 inches long by 18 high, brass geared wheels and movable spindle; with eight illustrations, viz. a double elastic brass ring, glass globe for mercury, etc., oblate and prolate spheres, cylinder, brass disk, brass ring, ring of chain, ....$8.00" 

   The apparatus was at Wittenberg University in Springfield, Ohio when I photographed it in the late nineteen seventies.
 



 
 

   The rotator at the right, with the Figure of the Earth demonstrator installed, was in the attic storage room of the Cornell University Physics Department when I visited in March 2003. When I left, it was being put back into the regular collection of demonstration apparatus, ready to work once more. 

   The base and the figure of the earth apparatus, apart from the driving disk, look very much like apparatus sold by E.S. Ritchie of Boston ca. 1860-1880; the whirling table, with a number of accessories, sold for $50.

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