made by the Venetians in the sixteenth century.  Huygens in the seventeenth century studied the laws of refraction and reflection and devised optical apparatus for various purposes.  However, it was not until the eighteenth century that any noteworthy 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 direction 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,