his umbrella forwards. The quicker his pace the more he
will find it advisable to tilt the umbrella. This analogy was stated by
Lalande before the days of umbrellas in the following words: "Je suppose
que, dans un temps calme, la pluie tombe perpendiculairement, et qu'on
soit dans une voiture ouverte sur le devant; si la voiture est en repos,
on ne recoit pas la moindre goutte de pluie; si la voiture avance avec
rapidite, la pluie entre sensiblement, comme si elle avoit pris une
direction oblique." Lalande's example, modified to suit modern conditions,
has been generally adopted by teachers, and in examinations candidates
produce graphic pictures of the stationary, the moderate-paced, and the
flying, possessors of umbrellas.

[Sidenote: Aberration.]

Applying it to the phenomenon which it is intended to illustrate, if light
is being received from a star by an earth, travelling across the direction
of the ray, the telescope (which in this case represents the umbrella)
must be tilted forward to catch the light. Now on reference to Fig. 4 it
will be seen that the earth is travelling across the direction of rays
from the star in March and September; and in opposite directions in the
two cases. Hence the telescope must be tilted a little, in opposite
directions, to catch the light; or, in other words, the star will appear
to be farthest south in March, farthest north in September. And so at last
the puzzle was solved, and the solution was found, as so often happens, to
be of the simplest kind; so simple when once we know, and so terribly hard
to imagine when we don't! It may comfort us in our struggles with minor
problems to reflect that Bradley manfully stuck to his problem for two or
three years. It was probably never out of his thoughts, waking or
sleeping; when at work it was the chief object of his labours, and when on
a pleasure party he was ready to catch at the slightest clue, in the
motion of a wind-vane on a boat, which might help him to the solution.

[Sidenote: Results of discovery.]

The discovery of aberration made Bradley famous at a bound. Oxford might
well be proud of her two Savilian Professors at this time, for they had
both made world-famous discoveries--Halley that of the periodicity of
comets, and Bradley of the aberration of light. How different their tastes
were and how difficult it would have been for either to do the work of the
other! Bradley was no great mathematician, and though he was quite ab