MATHEMATICAL TRACTS ON THE LUNAR AND PLANETARY THEORIES, THE FIGURE OF THE EARTH, PRECESSION AND NUTATION THE CALCULUS OF VARIATIONS, AND THE UNDULATORY THEORY OF OPTICS.

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Página 320 - This however is only true when the plates have a certain thickness : for, when they are very thin, the Ordinary and Extraordinary pencils are seen to have equal intensities. But the method of exhibiting polarized light which is most extensively used in experiments is, to reflect common light from unsilvered glass or any other transparent substance, solid or fluid. It is found that if the tangent of the angle of incidence is equal to the refractive index, the whole of the reflected light is polarized*...
Página 273 - We have, every reason,' he observes, ' to think that a part of the velocity of sound depends upon the circumstance that the law of elasticity of the air is altered by the instantaneous development of latent heat on compression, or the contrary effect on expansion. Now, if this heat required time for its development, the quantity of heat developed would depend...
Página 12 - The center of gravity of the Earth and Moon describes about the Sun, very nearly, an ellipse in one plane, and the area passed over by its radius vector is very nearly proportional to the time.
Página 329 - ... corresponding to the separate displacements : and then, by the reasoning in (10) and (11), any number of undulations, produced by vibrations in different directions, may co-exist without disturbing each other. PROP. 22. To explain the separation of common light into two pencils by doubly-refracting crystals : and to account for the polarization of the two rays in planes at right angles to each other. 106. We shall assume for the state of the particles of ether within a crystal, an arrangement...
Página 381 - Fresnel's rhomb. For here the light which is incident is resolved into two sets of vibrations at right angles to each other, and one of these is retarded in its phases by 90° more than the other ; which is precisely the effect of Fresnel's rhomb. There is however this difference between them. In...
Página 329 - ... (104), or at least possessing this property, that there are three directions* at right angles to each other, in which if a particle be disturbed, the resultant of the forces acting on it will tend to move it back in the same line in which the displacement is produced. These lines we suppose to be parallel to some lines determined by the form of the crystal. 107. Now in general the...
Página 273 - Now, if this heat required time for its development, the quantity of heat developed would depend upon the time during which the particles remained in nearly the same relative state, that is, on the time of vibration. Consequently, the law of elasticity would be different for different times of vibration, or for different lengths of waves ; and therefore the velocity of transmission would be different for waves of different lengths. If we suppose some cause which is put in action by the vibration...

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