ABSTRACT
The interferometric method of Fizeau permits the measurement of the coefficient of linear expansion of a solid of small dimensions. A sample is cut in the form of a plane parallel plate normal to the direction along which the expansion is to be measured. The whole assembly is placed in a thermostat. As a demonstration experiment, the expansion of a rod of dural may be shown with the help of a variant of the preceding method. This rod is surrounded by a heating wire. When the current is passed through the wire, the rings broaden, the new ones appearing at the centre. The principle of interference filters by reflection is the same as that of the filters by transmission. Their theory is that of the Fabry-Perot interferometer used in reflection with a parallel beam of light.
