leading eighteenth-century astronomer, convey more
clearly than any comment the actual state of the
meteorological learning at that time. That this ball
of fire, rushing "at a greater velocity than the swiftest
cannon-ball," was simply a mass of heated rock passing
through our atmosphere, did not occur to him, or at
least was not credited. Nor is this surprising when we
reflect that at that time universal gravitation had been
but recently discovered; heat had not as yet been
recognized as simply a form of motion; and thunder
and lightning were unexplained mysteries, not to be
explained for another three-quarters of a century.
In the chapter on meteorology we shall see how the
solution of this mystery that puzzled Halley and his
associates all their lives was finally attained.


BRADLEY AND THE ABERRATION OF LIGHT

Halley was succeeded as astronomer royal by a man
whose useful additions to the science were not to
be recognized or appreciated fully until brought to
light by the Prussian astronomer Bessel early in the
nineteenth century. This was Dr. James Bradley, an
ecclesiastic, who ranks as one of the most eminent
astronomers of the eighteenth century. His most remarkable
discovery was the explanation of a peculiar
motion of the pole-star, first observed, but not explained,
by Picard a century before. For many years a
satisfactory explanation was sought unsuccessfully by