Abstract
THEORY OF ASTRONOMICAL ABERRATION.—An interesting point connected with astronomical aberration was raised by M. Mascart in a paper presented to the Paris Academy of Sciences on November 2. It would at first appear that if observations demonstrated that the constant of aberration had precisely the same value for all stars, the velocity of light in space must be uniform. This interpretation, however, seems open to objections. Eclipses of Jupiter's satellites furnish a method for determining the velocity of light in the space contained within the earth's orbit, and, as is well known, the results obtained in this manner agree very well with those deduced from experiments made on the surface of the earth. But astronomical aberration depends only upon the relation of the velocity of the observer to that of the light in the region occupied by the instrument, and is unaffected by any variations in the velocity of propagation of the light-waves between the object observed and the earth. A real difference in the constant of aberration given by different stars would therefore indicate that the velocity of light was not uniform in the parts of space traversed by the earth. From this reasoning, M. Mascart is led to conclude that the values derived from the experiments, direct and astronomical, made to determine the velocity of light, should be limited to the space contained within the terrestrial orbit. The induction is certainly a legitimate one, and it must be admitted that to consider the velocity of light in interstellar space as uniform is to rely entirely on hypothesis.
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