Signedstamped on rear of mirror in an oval: O. FERNALD / BOSTON / FOUNDER.
Inscribedoval sticker: 7-3-45
FunctionA pair of such reflectors were used to demonstrate the transmission, reflection, and focusing of radiant heat or sound.
A watch ticking at the focus of one reflector could be heard at the focus of another receiving reflector.
To demonstrate that heat is a form of radiation, two such mirrors face each other. A red hot iron ball might be located at the focal point of one of the two mirrors, and some ignitable gun-cotton might be set at the focus of the other mirror.
Around the 1790s, this arrangement of mirrors was at the center of debates on the radiant nature of heat and the possible existence of "frigorific rays."
Historical AttributesInstruments with such oval stickers come from the Physics Department, Harvard University.
ProvenanceDepartment of Physics, Harvard University.
Related WorksFor a history of 'frigorific rays', the discussion of which was based on the use of such mirrors, see:
James Evans and Brian Bopp, "Pictet's Experiment: The apparent radiation and reflection of cold", in American Journal of Physics Vol 53, No. 8 (August 1985), pp. 737-753.