(3) of the
production of double refraction by irregular heating. These discoveries
were promptly recognized. So early as the year 1807 the degree of LL.D. was
conferred upon Brewster by Marischal College, Aberdeen; in 1815 he was made
a member of the Royal Society of London, and received the Copley medal; in
1818 he received the Rumford medal of the society; and in 1816 the French
Institute awarded him one-half of the prize of three thousand francs for
the two most important discoveries in physical science made in Europe
during the two preceding years. Among the non-scientific public his fame
was spread more effectually by his rediscovery about 1815 of the
kaleidoscope, for which there was a great demand in both England and
America. An instrument of higher interest, the stereoscope, which, though
of much later date (1849-1850), may be mentioned here, since along with the
kaleidoscope it did more than anything else to popularize his name, was
not, as has often been asserted, the invention of Brewster. Sir Charles
Wheatstone discovered its principle and applied it as early as 1838 to the
construction of a cumbrous but effective instrument, in which the binocular
pictures were made to combine by means of mirrors. To Brewster is due the
merit of suggesting the use of lenses for the purpose of uniting the
dissimilar pictures; and accordingly the lenticular stereoscope may fairly
be said to be his invention. A much more valuable practical result of
Brewster's optical researches was the improvement of the British lighthouse
system. It is true that the dioptric apparatus was perfected independently
by Fresnel, who had also the satisfaction of being the first to put it into
operation. But it is indisputable that Brewster was earlier in the field
than Fresnel; that he described the dioptric apparatus in 1812; that he
pressed its adoption on those in authority at least as early as 1820, two
years before Fresnel suggested it; and that it was finally introduced into
British lighthouses mainly by his persistent efforts.

Brewster's own discoveries, important though they were, were not his only,
perhaps not even his chief, service to science. He began literary work in
1799 as a regular contributor to the _Edinburgh Magazine_, of which he
acted as editor at the age of twenty. In 1807 he undertook the editorship
of the newly projected _Edinburgh Encyclopaedia_, of which the first part
appeared in 1808, and the last not until 1830. The wor