would be found at different parts of the orbits, and consequently the
disturbances would to a great extent neutralise each other, and
produce but little appreciable effect. As, however, Venus and the
earth come back every eight years to nearly the same positions at the
same points of their track, an accumulative effect is produced. For
the disturbance of one planet upon the other will, of course, be
greatest when those two planets are nearest, that is, when they lie
in line with the sun and on the same side of it. Every eight years a
certain part of the orbit of the earth is, therefore, disturbed by
the attraction of Venus with peculiar vigour. The consequence is
that, owing to the numerical relation between the movements of the
planets to which I have referred, disturbing effects become
appreciable which would otherwise be too small to permit of
recognition. Airy proposed to himself to compute the effects which
Venus would have on the movement of the earth in consequence of the
circumstance that eight revolutions of the one planet required almost
the same time as thirteen revolutions of the other. This is a
mathematical inquiry of the most arduous description, but the Plumian
Professor succeeded in working it out, and he had, accordingly, the
gratification of announcing to the Royal Society that he had detected
the influence which Venus was thus able to assert on the movement of
our earth around the sun. This remarkable investigation gained for
its author the gold medal of the Royal Astronomical Society in the
year 1832.

In consequence Of his numerous discoveries, Airy's scientific fame
had become so well recognised that the Government awarded him a
special pension, and in 1835, when Pond, who was then Astronomer
Royal, resigned, Airy was offered the post at Greenwich. There was
in truth, no scientific inducement to the Plumian Professor to leave