Foucault, who employed a scale of equal bright and dark alternate parts; it was found to be proportional to the aperture and independent of the focal length.
An effort at a more direct mechanical process is embodied in the inventions of Foucault which are at present being developed in Germany and Belgium; in this process the glass is drawn from the molten bath in the shape of flat sheets, by the aid of a bar of iron, previously immersed in the glass, the glass receiving its form by being drawn through slots in large fire-bricks, and being kept in shape by rapid chilling produced by the action of air-blasts.
Foucault, he engaged in a series of investigations on the interference of light and heat.
After their deaths he lived for some time at Caen under the roof of Nicolas Foucault (1643-1721), the intendant of Caen, himself no mean archaeologist; and there he began the publication (12 vols., 1704-1717) of Les mille et une nuits, which excited immense interest during the time of its appearance, and is still the standard French translation.
JEAN BERNARD LEON FOUCAULT (1819-1868), French physicist, was the son of a publisher at Paris, where he was born on the 18th of September 1819.
In Se p tember of that year he discovered that the force required for the rotation of a copper disk becomes greater when it is made to rotate with its rim between the poles of a magnet, the disk at the same time becoming heated by the eddy or "Foucault currents" induced in its metal.
Foucault invented in 1857 the polarizer which bears his name, and in the succeeding year devised a method of giving to the speculum of reflecting telescopes the form of a spheroid or a paraboloid of revolution.
Foucault died of paralysis on the 11th of February 1868 at Paris.
Comparisons of light grasp derived from small, fresh, carefully silvered surfaces are sometimes given which lead to illusory results, and from such experiments Foucault claimed superiority for the silvered speculum over the object-glass.
Foucault appears to have been the first to appreciate these advantages and to face the difficulty of designing a siderostat which, theoretically at least, fulfils the above-mentioned conditions.
It is, however, certain that the Foucault siderostat is not capable, in practice, of maintaining the reflected image in a constant direction with perfect uniformity on account of the sliding action on the arm that regulates the motion of the mirror; such an action must, more or less, take place by jerks.
Foucault, which, with improvements in detail, were based on the plan proposed by him.
In order to render visible the small waves employed, and which we may regard as deviations of a plane surface from its true figure, the method by which Foucault tested reflectors is suitable.
Foucault in 1849, by A.