perhaps have in their gardens - his louvre-boarded screen for
instruments. But the great achievement of his life was, of course,
in optics as applied to lighthouse illumination. Fresnel had done
much; Fresnel had settled the fixed light apparatus on a principle
that still seems unimprovable; and when Thomas Stevenson stepped in
and brought to a comparable perfection the revolving light, a not
unnatural jealousy and much painful controversy rose in France. It
had its hour; and, as I have told already, even in France it has
blown by. Had it not, it would have mattered the less, since all
through his life my father continued to justify his claim by fresh
advances. New apparatus for lights in new situations was
continually being designed with the same unwearied search after
perfection, the same nice ingenuity of means; and though the
holophotal revolving light perhaps still remains his most elegant
contrivance, it is difficult to give it the palm over the much
later condensing system, with its thousand possible modifications.
The number and the value of these improvements entitle their author
to the name of one of mankind's benefactors. In all parts of the
world a safer landfall awaits the mariner. Two things must be
said: and, first, that Thomas Stevenson was no mathematician.
Natural shrewdness, a sentiment of optical laws, and a great
intensity of consideration led him to just conclusions; but to
calculate the necessary formulae for the instruments he had
conceived was often beyond him, and he must fall back on the help
of others, notably on that of his cousin and lifelong intimate
friend, EMERITUS Professor Swan, of St. Andrews, and his later
friend, Professor P. G. Tait. It is a curious enough circumstance,
and a great encouragement to others, that a man so ill equipped
should have succeeded in one of the most abstract and arduous walks
of applied science. The second remark is one that applies to the