ue of such artificial-lighting devices depends both upon luminous
intensity and time of burning. Although long-burning is not generally
required in warfare, it is obvious that more than a momentary light is
usually needed. In general, high candle-power and long-burning are
opposed to each other, so that the most intense lights of this character
usually are of short duration. Typical performances of two flares of the
same composition are as follows:

Flare No. 1 Flare No. 2
Average candle-power 270,000 95,000
Seconds of burning 10 35
Candle-seconds 2,700,000 3,325,000
Cubic inches of compound 6 7
Candle-seconds per cubic inch 450,000 475,000
Candle-hours per cubic inch 125 132

The illuminating compound was the same in these two flares, which
differed only in the time allowed for burning. Of course, the
measurements of the luminous intensity of such flares is difficult
because of the fluctuations, but within the errors of the measurements
it is seen that the illuminating power of the compound is about the same
regardless of the time of burning. The light-source in the case of
burning powders is really a flame, and inasmuch as the burning end hangs
downward, more light is emitted in the lower hemisphere than in the
upper. The candle-power of the largest flares equals the combined
luminous intensities of 200 street arc-lamps or of 10,000 ordinary
40-watt tungsten lamps such as are used in residence lighting.

It is interesting to note the candle-hours obtained per cubic inch of
compound and to find that the cost of this light is less than that of
candles at the present time and only five or ten times greater than that
of modern electric lighting.

Illuminating shells in use during the recent war were designed for
muzzle velocities as high as 2700 feet per second and were gaged to
ignite at any distance from a quarter of a mile to several miles. The
maximum range of illuminating shells fired from rifles was about 200
yards; for trench mortars about one mile; and from field and naval guns
about four miles.

The search-light has long been a valuable aid in warfare and during the
recent conflict considerable attention was given to its development and
application. It is used chiefly for detecting and illuminating distant
targets, but this covers a w