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consists of hydrogen gas combined with phosphorus and sulphur, which being exceedingly inflammable, may be set on fire by the friction of the air in a breeze too gentle for agitating the branches or rustling the leaves. The motion of a human being through an atmosphere strongly impregnated with those highly inflammable gases, may be sufficient to produce a train of the cold blue flame.
It is from the decomposition of animal and vegetable matters that those gases are produced. The quantity of small animals-chiefly of the insect tribes, that are continually perishing in marshesby falling from their island habitations in their rushes and reeds into the water between, is much greater than would readily be
supposed; and when those waters are shallow, and the air and light, in consequence, act powerfully upon them, there are materials and means enough for the production of ten times the number of ignes fatui, that ever were observed. Churchyards are very favourable for their appearance; and hence probably the reason why they have been associated with spirits, and considered objects of terror, while they are in themselves not only perfectly harmless, but exceedingly beautiful, especially when seen in lonely places and amid trees.
In tropical countries, where the action of the sun is more powerful during the day, and longer suspended during the night than with us, and where consequently both growth and decomposition go on much more rapidly, those airy meteors of the night are much more common than they are with us. They are more common at sea, too, than they are on land; though there they seldom rise above the surface unless the water is agitated. But when that is done, in certain states of the weather, namely, after long calms, when the water has not been much disturbed, there is a ripple of light at the bows of the vessel, and her wake bears some resemblance to the tail of a comet. Every splash of the oars flings radiance, and a hand skilfully dipped in the water appears to be kindling. There seems little reason to doubt, that all those lights are produced by decomposition, whether of the ultimate destruction of dead animals or of the separation of waste in living ones; and that they are nothing more than some of the highly inflammable gaseous compounds kindled by the friction of motion. That they do exist in living animals is seen in the various species of fire-flies, which in some parts of the tropical countries make the evening sky as brilliant as if the whole heavens were hung with countless myriads of little lamps, and all those lamps were dancing in mazes of incessant motion. We have no luminous
flying insect in this country; but the female GLOW-WORM, which is not uncommon under hedges in the warmer places of England, and at the warm season of the year, emits a beautiful bluish white light, which appears much brighter in consequence of the dark and shady places in which it is seen. The male of the glow-worm is a winged insect, which flies low in the evenings, but emits no light.