ABSTRACT
Some of the contrivances described have for their end and object the communication of motion to certain bodies, others the arrangement of materials in some definite form, and all are essentially associated with the idea of what is called matter. The diversity and magnificence of the spectacles which, by day as well as by night, are revealed to the reader by the agency of light, have been the theme of the poet in every age and in every country. M. Foucault’s method is similar in principle to that used by Wheatstone in the measurement of the velocity of electricity. Instruments of various forms have been devised for examining the phenomena of polarized light. The point in question is fortunately one extremely easy of experiment, since the people have simple means of producing light in which the vibrations corresponding to only one colour are present.
