ght had been very
favourite subjects with him, and he had written and lectured
frequently upon them. In the construction of the new and powerful
telescopes and other optical instruments required from time to time
this knowledge was very essential, for in its instrumental equipment
the Greenwich Observatory was entirely remodelled during his tenure of
office. And in many of the matters referred to him, as for instance
that of the Lighthouses, a thorough knowledge of Optics was most
valuable. He had made a great study of the theory and construction of
clocks, and this knowledge was invaluable to him at Greenwich in the
establishment of new and more accurate astronomical clocks, and
especially in the improvement of chronometers. He had carefully
studied the theory of pendulums, and had learned how to use them in
his experiments in the Cornish mines. This knowledge he afterwards
utilized very effectively at the Harton Pit in comparing the density
of the Earth's crust with its mean density; and it was very useful to
him in connection with geodetic surveys and experiments on which he
was consulted. And his mechanical knowledge was useful in almost
everything.

The subjects (outside those required for his professional work) in
which he took most interest were Poetry, History, Theology,
Antiquities, Architecture, and Engineering. He was well acquainted
with standard English poetry, and had committed large quantities to
memory, which he frequently referred to as a most valuable acquisition
and an ever-present relief and comfort to his mind. History and
theology he had studied as opportunity offered, and without being
widely read in them he was much at home with them, and his powerful
memory made the most of what he did read. Antiquities and architecture
were very favourite subjects with him. He had visited most of the
camps and castles in the United Kingdom and was never tired of tracing
their connection with ancient military events: and he wrote several
papers on this subject, especially those relating to the Roman
invasions of Britain. Ecclesiastical architecture he was very fond of:
he had visited nearly all the cathedrals and principal churches in
England, and many on the Continent, and was most enthusiastic on their
different styles and merits: his letters abound in critical remarks on
them. He was extremely well versed in mechanics, and in the principles
and theory of construction, and took the greatest interest in large