When the recent war broke out science responded to the call and under the stress of feverish necessity compressed the normal development of a half-century into a few years.  The airplane, in 1914 a doubtful plaything of daredevils, emerged from the war a perfected thing of the air.  Lighting did not have the glamor of flying or the novelty of chemical warfare, but it progressed greatly in certain directions and served well.  While artificial lighting conducted its unheralded offensive by increasing production in the supporting industries and helped to maintain liaison with the front-line trenches by lending eyes to transportation, it was also doing its part at the battle front.  Huge search-lights revealed the submarine and the aerial bomber; flares exposed the manoeuvers of the enemy; rockets brought aid to beleaguered vessels and troops; pistol lights fired by the aerial observer directed artillery fire; and many other devices of artificial light were in the fray.  Many improvements were made in search-lights and in signaling devices and the elements of the festive fireworks of past ages were improved and developed for the needs of modern warfare.

Night after night along the battle front flares were sent up to reveal patrols and any other enemy activity.  On the slightest suspicion great swarms of these brilliant lights would burst forth as though flocks of huge fireflies had been disturbed.  They were even used as light barrages, for movements could be executed in comparative safety when a large number of these lights lay before the enemy’s trenches sputtering their brilliant light.  The airman dropped flares to illuminate his target or his landing field.  The torches of past parades aided the soldier in his night operations and rockets sent skyward radiated their messages to headquarters in the rear.  The star-shell had the same missions as other flares, but it was projected by a charge of powder from a gun.  These and many modifications represent the useful applications of what formerly were mere “fireworks.”  Those which are primarily signaling devices are discussed in another chapter, but the others will be described sufficiently to indicate the place which artificial light played in certain phases of warfare.

The illuminating compounds used in these devices are not particularly new, consisting essentially of a combustible powder and chemical salts which make the flame luminous and give it color when desired.  Among the ingredients are barium nitrate, potassium perchlorate, powdered aluminum, powdered magnesium, potassium nitrate, and sulphur.  One of the simplest mixtures used by the English is,

Barium nitrate          37 per cent. 
Powdered magnesium      34 per cent. 
Potassium nitrate       29 per cent.

The magnesium is coated with hot wax or paraffin, which not only acts as a binder for the mixture when it is pressed into its container but also serves to prevent oxidation of the magnesium when the shells are stored.  The barium and potassium nitrates supply the oxygen to the magnesium, which burns with a brilliant white flame.  The potassium nitrate takes fire more readily than the barium nitrate, but it is more expensive than the latter.