Another pyrotechnic invention responsible for the saving of many lives is the Hale’s Light apparatus. This apparatus is fitted to a lifebuoy, which is arranged for launching from a vessel’s bridge; the act of launching ignites a flare, enabling the person in the water to see the buoy and the rescuing boat to pick them up. The practical use to which fireworks have been put on land are many. Probably that which comes most readily to the mind is the sound signal or alarm. Many fire brigades whose members are volunteers and therefore scattered use aerial maroons to warn and call them for duty. These maroons became familiar to Londoners during the air raid period in the late war. The maroon has also been adopted for firing with a trip line as a burglar alarm, or for protecting game preserves or similar purposes. Another well-known pyrotechnic sound signal is the fog signal used on the railways, which consists of a tinned iron envelope containing a mixture of chlorate of potash and red phosphorus. It is secured in position on the rail by two lead clips provided for the purpose, and is fired by percussion on the impact of the engine wheel. Bird scarers, consisting of a series of single crackers connected by a time fuse, and so arranged as to fire at regular intervals, have been much used for the protection of seed and crops. The miner’s squib and chieza stick or fuse lighter are to all intents port-fires for lighting the fuse in blasting operations in mines, their form and composition being adapted to the particular circumstances of their use. [Illustration: Crystal Palace. From a photograph taken by the light of a magnesium shell. The crowd at “Brock’s Benefit” (64,000 persons present).] The use of pyrotechnic compositions for photographic purposes is well known; those in use at the present generally contain magnesium, which has greater actinic value than any other firework composition. Magnesium lights fitted up to fire with a trip line have been successfully used for obtaining photographs of big game in their native surroundings at night. Smoke pyrotechnically produced has for several years been used for the testing of drains, and recently successful experiments have been carried out establishing the value of smoke as a protection for fruit blossom against frost. It has also been used as an insecticide for use against various kinds of parasites; a poisonous smoke has been found of great use in the dislodging and exterminating of rats. Another agricultural use of pyrotechnic, or in this case perhaps more correctly explosive composition, is the use of explosive cartridges for ploughing; that is, cartridges are exploded at a certain depth in the ground, the effect being to break up the subsoil. The explosive used is a mild and cheap form of dynamite.