nity-House of London followed next in
adopting the improved system, and a revolving dioptric light of the
first order was erected at the Star Point in Devonshire.

In the lighthouses of this country sperm-oil is the most usual fuel.
In France[6] an oil is burned called Colza oil, expressed from the
seeds of a species of wild cabbage. In the lighthouses on the
Mediterranean olive-oil is used. In a few lighthouses near large towns
coal-gas has been advantageously adopted. Much also has been said in
favour of the Drummond and Voltaic lights, which, on account of their
prodigious intensity would appear to be most desirable; but the
uncertainty which attends their exhibition renders it at present
impossible to adopt them: but there is a yet more fatal objection--the
smallness of the flame renders them wholly inapplicable to dioptric
instruments, which require a great body of flame in order to produce a
degree of divergency sufficient to render the duration of the flash
in revolving lights long enough to answer the purpose of the mariner.

In the year 1835, Mr. Gurney proposed a lamp of great power in which
the flame of oil or wax was sustained by streams of oxygen gas, a
method said to be more economical than the combustion of oil in
atmospheric air. The Trinity House entertained the proposal, and
instituted a number of experiments. In applying this light to
reflectors it is intended to use three small flames, each about
three-eighths of an inch in diameter, productive, it is said, of an
effect equal to that of ten Argand lamps. But for lenses the burner
has seventeen films of flame, and is said to possess six times the
power of the Fresnel lamp.

In the year 1840, Captain Basil Hall instituted a series of
experiments to ascertain whether the well-known superior brilliancy of
a revolving light could not be obtained for a fixed or continuous
light, that is, for one equally visible in all directions at the same
moment. His idea was, that by giving a certain velocity of revolution
to a series of lenses round a fixed light, as in Fresnel's
arrangement, a continuity of illuminative power, equal almost in
brilliancy to that of a slowly revolving light, might be produced. The
apparatus was arranged so as to cause a series of eight lenses one
foot in diameter and three feet focal distance to revolve with any
velocity up to sixty revolutions per minute round a central lamp. The
light from this lamp being concentrated by refraction