teworthy attempts were made to
control artificial light for practical purposes. Dollond in 1757 was the
first to make achromatic lenses by using combinations of different
glasses. Lavoisier in 1774 made a lens about four feet in diameter by
constructing a cell of two concave glasses and filling it with water and
other liquids. It is said that he ignited wood and melted metals by
concentrating the sun's image upon them by means of this lens. About
that time Buffon made a built-up parabolic mirror by means of several
hundred small plane mirrors set at the proper angles. With this he set
fire to wood at a distance of more than two hundred feet by
concentrating the sun's rays. He is said also to have made a lens from a
solid piece of glass by grinding it in concentric steps similar to the
designs worked out by Fresnel seventy years later. These are examples of
the early work which laid the foundation for the highly perfected
control of light of the present time.

While engaged in the survey of Ireland, Thomas Drummond in 1826 devised
apparatus for signaling many miles, thus facilitating triangulation.
Distances as great as eighty miles were encountered and it appeared
desirable to have some method for seeing a point at these great
distances. Gauss in 1822 used the reflection of the sun's image from a
plane mirror and Drummond also tried this means. The latter was
successful in signaling 45 miles to a station which because of haze
could not be seen, or even the hill upon which it rested. Having
demonstrated the feasibility of the plan, he set about making a device
which would include a powerful artificial light in order to be
independent of the sun. In earlier geodetic surveys Argand lamps had
been employed with parabolic reflectors and with convex lenses, but
apparently these did not have a sufficient range. Fresnel and Arago
constructed a lens consisting of a series of concentric rings which were
cemented together, and on placing this before an Argand lamp possessing
four concentric wicks, they obtained a light which was observed at
forty-eight miles.

Despite these successes, Drummond believed the parabolic mirror and a
more powerful light-source afforded the best combination for a
signal-light. In searching for a brilliant light-source he experimented
with phosphorus burning in oxygen and with various brilliant
pyrotechnical preparations. However, flames were unsteady and generally
unsuitable. He then turned in the dir