ection which led to his development
of the lime-light. In his first apparatus he used a small sphere of lime
in an alcohol flame and directed a jet of oxygen through the flame upon
the lime. He thereby obtained, according to his own description in 1826,

a light so intense that when placed in the focus of a reflector
the eye could with difficulty support its splendor, even at a
distance of forty feet, the contour being lost in the
brilliancy of the radiation.

He then continued to experiment with various oxides, including zirconia,
magnesia, and lime from chalk and marble. This was the advent of the
lime-light, which should bear Drummond's name because it was one of the
greatest steps in the evolution of artificial light.

By means of this apparatus in the survey, signals were rendered visible
at distances as great as one hundred miles. Drummond proposed the use of
this light-source in the important lighthouses at that time and foresaw
many other applications. The lime-light eventually was extensively used
as a light-signaling device. The heliograph, which utilizes the sun as a
light-source, has been widely used as a light-signaling apparatus and
Drummond perhaps was the first to utilize artificial light with it. The
disadvantage of the heliograph is the undependability of the sun. With
the adoption of artificial light, various optical devices have come into
use.

Philip Colomb perhaps is deserving of the credit of initiating modern
signaling by flashing a code. He began work on such a system in 1858 and
as an officer in the British Navy worked hard to introduce it. Finally,
in 1867, the British Navy adopted the flashing-system, in which a
light-source is exposed and eclipsed in such a manner as to represent
dots and dashes analogous to the Morse code. At first the rate of
transmission of words was from seven to ten per minute. Recently much
more sensitive apparatus is available, and with such devices the rate is
limited only by the sluggishness of the visual process. This initial
system was very successful in the British Navy and it was soon found
that a fleet could be handled with ease and safety in darkness or in
fog. Inasmuch as the "dot-and-dash" system requires only two elements,
it may be transmitted by various means. A lantern may be swung in short
and long arcs or dipped accordingly.

The blinker or pulsating light-signal consists of a single light-source
mechanically occulted. It is co