It will Le seen that Bernoulli is a thorough Cartesian in spirit not only does he reject action at a distance, but he insists that even the elasticity of his aether shall be explicable in terms of matter and motion. The elasticity which the aether appears to possess, and in virtue of which it is able to transmit vibrations, is really due to the presence of these whirlpools for, owing to centrifugal force, each whirlpool is continually striving to dilate, and so presses against the neighbouring whirlpools. This defect his son now proceeded to remove.Īll space, according to the younger Bernoulli, is permeated by a fluid aether, containing an immense number of excessively small whirlpools. This is the same equation as that which expresses the law of refraction, and the elder Bernoulli conjectured that a theory of light might be based on it but he gave no satisfactory physical reason for the existence of forces along the incident and refracted rays. Where i and r denote the angles made by these directions with the normals to the plane.
#Meridian 157 chapter 3 ending explained free#
If two opposed forces whose ratio is μ maintain in equilibrium a particle which is free to move only in a given plane, it follows from the triangle of forces that the directions of the forces must obey the relation 1748), had made in 1701 to connect the law of refraction with the mechanical principle of the composition of forces.
was in 1736 awarded the prize of the French Academy, His: ideas seem to have been originally suggested by an attempt which his father, the elder John Bernoulli ( b. But some attention must be given to a suggestive study of the aether, for which the younger John Bernoulli ( b. to the brilliance of its record in respect of electrical researches. primarily astronomical rather than optical, the eighteenth century was decidedly barren, as regards both the experimental and the theoretical investigation of light in curious contrast. With the exception of Bradley's discovery, which was. Observations such as Bradley's will therefore enable us to deduce the ratio of the mean orbital velocity of the earth to the velocity of light, or, as it is called, the constant of aberration from its value Bradley calculated that light is propagated from the sun to the earth in 8 minutes 12 seconds, which, as he remarked, "is as it were a Mean betwixt what had at different times been determined from the eclipses of Jupiter's satellites." The angle BCA measures the difference between the real and apparent positions of the object and it is evident from the figure that the sine of this angle is to the sine of the visible inclination of the object to the line in which the eye is moving, as the velocity of the eye is to the velocity of light. The tube of a telescope must therefore be pointed in the direction BC, in order to receive the rays from an object whose light is really propagated in the direction CA. Then the corpuscle of light, by which the object is discernible to the eye at A, would have been at C when the eye was at B. Thus, let CA denote a ray of light, falling on the line BA and suppose that the eye of the observer is travelling along BA, with a velocity which is to the velocity of light as BA is to CA. Such an effect could not be explained as a result of parallax, and eventually Bradley guessed it to be due to the gradual propagation of light. 1762), at that time Savilian Professor of Astronomy at Oxford, sent to the Astronomer Royal (Halley) an "Account of a new discovered motion of the Fix'd Stars." In observing the star γ in the head of the Dragon, he had found that during the winter of 1725–6 the transit across the meridian was continually more southerly, while during the following summer its original position was restored by a motion northwards. As it happened, the chief optical discovery of this period tended to support the latter theory, by which it was first and most readily explained. The Luminiferous Medium, from Bradley to Fresnel.Īlthough Newton, as we have seen, refrained from committing himself to any doctrine regarding the ultimate nature of light, the writers of the next generation interpreted his criticism of the wave-theory as equivalent to an acceptance of the corpuscular hypothesis.
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