His memoir on this subject fully ex pounds the method of
finding the weight of a planet from observations of the movements of
a satellite by which the planet is attended. This is, indeed, a
valuable investigation which no student of astronomy can afford to
neglect. The ardour with which Airy devoted himself to astronomical
studies may be gathered from a remarkable report on the progress of
astronomy during the present century, which he communicated to the
British Association at its second meeting in 1832. In the early
years of his life at Cambridge his most famous achievement was
connected with a research in theoretical astronomy for which
consummate mathematical power was required. We can only give a brief
account of the Subject, for to enter into any full detail with regard
to it would be quite out of the question.
Venus is a planet of about the same size and the same weight as the
earth, revolving in an orbit which lies within that described by our
globe. Venus, consequently, takes less time than the earth to
accomplish one revolution round the sun, and it happens that the
relative movements of Venus and the earth are so proportioned that in
the time in which our earth accomplishes eight of her revolutions the
other planet will have accomplished almost exactly thirteen.
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