The concept of an ether to convey light probably seems strange and unnecessary to an optical engineer today. However, until well into the nineteenth century it seemed to be necessary to depend on a hypothetical fluid to convey all physical substances. Sound, of course, is conveyed by the air. Heat was considered as a substance called “caloric.” Fire was conceived as “phlogiston.” Electricity and magnetic fields were carried by “effluvia.” Accordingly, the concept of an ether to convey the vibrations of light seemed to be quite reasonable.
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