k at Greenwich.]

It seems needless to mention his work as Astronomer Royal, but I will give
quite briefly a summary of what he accomplished, and then recall a
particular incident, which shows how far ahead of his generation his
genius for observation placed him. The summary may be given as follows.
We owe to Bradley--

1. A better knowledge of the movements of Jupiter's satellites.

2. The orbits of several comets calculated directly from his own
observations, when such work was new and difficult.

3. Experiments on the length of the pendulum.

4. The foundation of our knowledge of the refraction of our atmosphere.

5. Considerable improvements in the tables of the moon, and the promotion
of the method for finding the longitude by lunar distances.

6. The proper equipment of our national Observatory with instruments, and
the use of these to form the basis of our present knowledge of the
positions and motions of the stars.

Many men would consider any one of these six achievements by itself a
sufficient title to fame. Bradley accomplished them all in addition to his
great discoveries of aberration and nutation.

[Sidenote: Might have found variation of latitude.]

And with a little more opportunity he might have added another great
discovery which has shed lustre on the work of the last decade. We said
earlier in this chapter that the axis of the earth may move in one or two
ways. Either it may point to a different star, remaining fixed relatively
to the earth, as in the nutation which Bradley discovered; or it may
actually change its position in the earth. This second kind of movement
was believed until twenty years ago not to exist appreciably; but the
work of Kuestner and Chandler led to the discovery that it did exist, and
its complexities have been unravelled, and will be considered in the sixth
chapter. Now a century and a half ago Bradley was on the track of this
"variation of latitude." His careful observations actually showed the
motion of the pole, as Mr. Chandler has recently demonstrated; and,
moreover, Bradley himself noticed that there was something unexplained.
Once again there was a _residuum_ after (first) aberration and (next)
nutation had been extracted from the observations; and with longer life he
might have explained this residuum, and added a third great discovery to
the previous two. Or another coming after him might have found it; but
after the giant came men who could not tread in his