53S 



PHOSPHORESCENCE. 



rescent quality. \\ lirn Uie electric discharge is 

 transmitted along the surfaces of certain bodies, or a 

 little above them, a somewhat durable phosphores- 

 cence is produced. Sulphate of barytes gives a 

 bright green light, acetate of potash a brilliant green 

 light, and rock crystal, a red and then white light. 

 Temperature lias a marked effect on the emission of 

 light by these bodies. When they are shining, the 

 luminous appearance ceases if they are exposed to 

 the cold of a freezing mixture. It becomes more 

 vivid by applying heat ; and if it has ceased, it may 

 be renewed by applying a stronger heat, so that a 

 piece of any solar phosphorus, which has apparently 

 lost its power, may by heat be agnin made to shine. 

 Some of the phosphorescent bodies, just mentioned, 

 after their luminousness is over, upon partially heat- 

 ed iron, yield on fusion a very vivid light. Lime is 

 the substance possessing this property in the most 

 remarkable degree. If a piece of calcareous spar is 

 placed on charcoal before the compound blowpipe, 

 it emits a light so vivid and white that it can scarce 

 ly be looked upon. The following fluids have been 

 found by doctor Brewster to be phosphorescent when 

 poured into a cup of heated iron : Albumen (white 

 of an egg) diluted in water, isinglass in solution, 

 saliva, soap and water, solution of rhubarb, do. of 

 common salt, do. of nitre, tallow (the phosphores- 

 cence of which may be observed when a candle is 

 extinguished in a dark room), alcohol, oil of dill- 

 seeds and oil of olives. Several cry ptogamous plants 

 have been observed to be luminous in the dark. 

 The Rhizomorpha phosphoreus found in the mines of 

 Hesse exhibits light when the extremities of the plant 

 are broken. Other species of Rhizomorpha have 

 also appeared phosphorescent to the miners. But 

 marine animals are the most remarkable for this pro- 

 perty ; and to them is now fairly attributed the once 

 mysterious phosphorescence of the ocean. This 

 phenomenon is occasionally observable every where 

 at sea ; but it is in warmer regions and more southern 

 latitudes, that it attains its greatest degree of bril- 

 liancy and beauty. In these parts it has been thus 

 described by a scientific observer : "At onetime, 

 the evening serene and delightful, a pleasant breeze 

 iust filling the sails, and the bow of the vessel throw- 

 ing the water to each side, as it gracefully parts the 

 yielding waves, all round the ship, far as the eye 

 can reach, may be seen innumerable bright spots of 

 light rising to the surface, and again disappearing, 

 like a host of small stars dancing and sparkling on 

 the bosom of the sea. At another time, the night 

 dark and lowering, a fresh breeze urging the ship 

 rapidly onwards through her pathless track, upon 

 looking over the stern, in addition to the smaller 

 specks just now mentioned, large globes of living 

 fire may be seen wheeling and dancing in the smooth 

 water in the wake of the rudder ; now, at a great 

 drptli shining through the water, then rising rapidly 

 to the surface, they may be seen, as they reach the 

 top of the wave, flashing a bright spark of light, suf- 

 ficient almost to dazzle the eyes of the beholder ; and 

 now, again, they may be traced floating majestically 

 along, till they gradually disappear in the darkness 

 of the water in the distance. At other times, again, 

 when light rain is falling, or perhaps previously to 

 the rain coming on, when a light nimbose cloud is 

 overspreading the sky, upon the water being agitat- 

 ed by the ship passing through it, or curled up by a 

 rope towing overboard in a bight, a beautiful, gene- 

 ral luminousness is diffused all around, bright enough 

 to illuminate the whole ship's side, and the lower 

 large sails which may be set at the time ; and it is 

 no unusual occurrence to have this appearance so 

 bright, that a person with little difficulty, and near 

 the surface of the water, might be enabled to read." 



That all this light is afforded by little animalcule* 

 there cannot be the smallest room for doubt ; for 

 they have been caught in the very act of giving out 

 the luminous appearance, and in vast numbers ; and 

 in every instance where the water has been properly 

 examined when luminous, they have been seen in 

 great quantities ; while, on the other hand, when the 

 water has not been luminous, they have not been 

 visible. They have been described and figured by 

 naturalists, who have studied them by the aid of 

 powerful microscopes ; and they are found to belong 

 to the mollusca, the vermes, the Crustacea and the 

 zoophytes. Light is also emitted from certain land 

 insects, as from the lightning-bug and the glow-worm. 

 A kind of phosphorescence, still different, is that 

 observed in decomposing animal and vegetable 

 matter. It appears during the putrefaction of fishes, 

 especially, but has been observed also from the flesh 

 of quadrupeds. Our woods during autumn frequently 

 exhibit a high degree of luminousness in light rotten 

 wood. 



The first animal possessing the property of 

 phosphorescence, which attracted the attention of 

 naturalists, was the pholas dactylus, a species of 

 chonchiferous mollusca, protected by a testaceous 

 shell (see Conchology, p. 380, pi. 19, f. 14). This 

 quality in the pholas was first observed by Pliny, and 

 has since been confirmed by Reaumur. Pliny says 

 that the whole substance of the animal is charged 

 with a fluid which has the property of emitting a 

 phosphorescent light; and that it will illuminate 

 any substance which it touches. This is the only 

 testaceous mollusca which has the property of 

 evolving a phosphorescent light. Dr Priestley says, 

 " This fish illuminates the mouth of the person who 

 eats it: and it is remarkable, that, contrary to the 

 nature of other fish, which give light when they tend 

 to putrescence, this is more luminous the fresher it 

 is; when dried its light will revive on being moist- 

 ened either with salt water or fresh; brandy, how- 

 ever immediately extinguishes it." 



We have given representations of a few luminous 

 animals in plate 32. 



There are three species of beetle, of the genus 

 Elater, which have the property of emitting light. 

 These are the E. noctilucus, E. phosphoreus, and E. 

 Ignitus. 



The great fire-fly (elater noctilucus) fig. 21, is an 

 inhabitant of the savannas of most of the warmer 

 parts of America, where they are to be seen in 

 great abundance, and also about the woods of several 

 of the West India islands. They are extremely 

 luminous in the dark, the light proceeding chiefly 

 from four parts; namely, from two glandular spots 

 behind the eyes, and one under each wing. But 

 they have the property of interrupting this light at 

 pleasure, when these glandular spots become per- 

 fectly opaque. When the rings of the abdomen are 

 forced a little asunder, the same luminous appearance 

 will be seen to issue indiscriminately from every part 

 of their interior. 



A person may with great ease read the smallest 

 print by the light of one of these insects held between 

 the fingers, and gradually moved along the lines, 

 with the luminous spots above the letters ; but if 

 eight or ten of them be put into a phial, the light 

 will be sufficiently great to admit of writing by it. 

 Oviedo says, that the Indians travel in the night 

 with these insects fixed to their hands and feet; and 

 that they spin, weave, paint, dance, &c., by their 

 light. 



The elaters are seldom to be seen abroad during the 

 day, for, except in the night, they are so inanimate, as 

 even scarcely to exhibit any sign* of life. The Indians 

 principally value them from their hmitinfc and do- 



