Leslie's Cube
   Here, what should be Leslie's Cube, is Leslie's Hexagon! In its usual form, the three pairs of opposite sides of the cube are covered with materials and finishes of differing emissivities: a white surface and a black surface; a rough finish and a smooth finish; brass and silver or chromium. 

   The device is filled with hot water and placed between the two bulbs of a Differential Thermoscope, which indicates which surface is radiating energy at the greater rate. 

   This example is at the Collection of Historical Scientific Instruments at Harvard University.

   However, Leslie's Cube can still be used for experiments. In an introductory project laboratory at St. Patrick's College in Maynooth, Ireland, I discovered a differential thermopile about 100 years old being used to make measurements with a modern Leslie's Cube. 
   In a third configuration, the cube is reduced to a disk, with one side shiny and the other dull black. The drum containing the hot water is 9 cm in diameter, and is held on a solid rod. 

   Even with hot tap water, the differential thermoscope responds when this "cube" is placed between its bulbs.

   Although it is unmarked, this item appears in the 1900 Max Kohl catalogue as "Weinhold's steam-case for radiation experiments" and sold for 11 marks (about $3)

   The apparatus is in the Greenslade Collection.

Another form of Leslie's Cube is Ritchie's Apparatus.

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