| The transparent glass cone will produce a circular spectrum,
while the glass pyramid will produce a set of four spectra.
Most of this and similar apparatus that I have seen in American collections is French. For example, both of the Union College conical prisms at the right were made by the firm of Jules Duboscq of Paris.
Note that one of the conical prisms at Union is made of
black glass, and so must be a device for illustrating the properties of
light reflected from a smooth, conical surface
The prisms below were all made by Lerebours and Secretan of Paris.
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