instrument and Halley with the new. The results
showed slightly in the younger man's favor, but not
enough to make it an entirely convincing demonstration.
The explanation of this, however, did not lie in
the lack of superiority of the telescopic instrument,
but rather in the marvellous skill of the aged Hevelius,
whose dexterity almost compensated for the defect of
his instrument. What he might have accomplished
could he have been induced to adopt the telescope can
only be surmised.

Halley himself was by no means a tyro in matters
astronomical at that time. As the only son of a
wealthy soap-boiler living near London, he had been
given a liberal education, and even before leaving college
made such novel scientific observations as that of
the change in the variation of the compass. At nineteen
years of age he discovered a new method of determining
the elements of the planetary orbits which
was a distinct improvement over the old. The year
following he sailed for the Island of St, Helena to make
observations of the heavens in the southern hemisphere.

It was while in St. Helena that Halley made his
famous observation of the transit of Mercury over the
sun's disk, this observation being connected, indirectly
at least, with his discovery of a method of determining
the parallax of the planets. By parallax
is meant the apparent change in the position of an object,
due really to a change in the position of the observer.