Living lights

As to the value and use of the gift of luminosity possessed by various animals, we can only surmise. Many interesting theories have been suggested, none of which, however, seem to stand the test of practical application. Some naturalists believe that the light of certain invertebrates is a warning. As an example, the jelly-fishes have a terrible array of stings; and it is supposed that fishes once stung, remember the light of these forms, and avoid them in the future. If this were true, many helpless animals, as the salpa and others, would also find protection in the lesson taught by the jelly-fishes.

It is a poor rule that will not work both ways; and we might well ask, if nature supplies these lights as warnings, why the physalia, the most terrible of all these forms, has not been thus provided. Phipson mentions it as a phosphorescent animal, but in the thousands that I have observed during a long residence in the physalia country, I never saw one give out light; hence I assume that if they are luminous, it is only on certain occasions. It might be considered that the vivid colors of this attractive creature constituted a warning; but even this does not hold, as I have found all kinds of pelagic fishes in their toils, and even a turtle and many small fishes bite readily at the deadly tentacles.

It is well known that the sunfish (Orthagoriscus), lump-fish, and dogfish all attack jelly-fishes, perhaps in default of better food; and far from being afraid of light, all fishes are attracted by it. It is evident, that, if jelly-fishes possess eyes, they must be able to distinguish others of their kind; hence their phosphorescence may possibly be a simple signal language, if so we may term it, by which they may find one another; or, having its origin in the nervous functions of the animal, the light may be unconsciously emitted, and have no more significance than a blush or sudden pallor upon the human face. Whatever may be the value of the light to themselves, it is of obvious use to other animals. It assists in the general illumination of the deep recesses of the ocean; and, in the case of jelly-fishes, certainly marks their position, and thus aids the whalebone whales when feeding at night at depths from the surface where little light penetrates.

The various colored lights seen upon certain crustaceans and worms, and their peculiar position, point to the possible belief that they may be signals, constituting a primitive means of communication; also of use to the animals in lighting their way, as we have seen in the case of the pyrophorus. The lights of fishes, whatever may have been the object of nature, serve several distinct purposes: to draw the attention of enemies, to attract prey, and to illumine the gloom about them. Any one who has fished at night by torchlight well knows the attraction that light has for fishes of all kinds, and when submarine electric lights have been watched, groups of fishes and squids have been observed about them; so it is evident that predatory fishes possessing lights have in their lure a decided advantage.

Actual experiment has shown that the electric light can be seen ninety-nine feet under water. The soft rays of animal phosphorescence would not penetrate so far, but would be powerful enough to illumine the water for some distance about them.

The deep-sea fishes which are not remarkable for their phosphorescence, or do not possess it at all, have feelers in many instances, and grope about like blind men: while others have eyes that not only see, but are possible emitters of light themselves. In the case of the predatory shark captured by Bennett, we may assume that the light was an effective lure: but the same will not apply to the brilliant scopelus and other delicate little creatures almost completely defenceless; so that it will be seen that it is as difficult to lay down fixed rules for the use of the light as to explain the cause of its production. The phosphorescence of corals and their allies,—gorgonias, sea-anemones, etc., may serve to attract prey. The minute crustaceans, so valuable to food fishes, are by their unfortunate gift rendered visible to their enemies, and the same may apply to many of the worms; while in a certain species of the genus Polynæ, we have seen that the phosphorescent scales which it throws off may be used to delude its enemies, just as when certain lizards cast off their tails, and dart away, leaving them wriggling and squirming, to attract the attention of their pursuers. Certain crustaceans have luminous bands or spots which undoubtedly serve as lanterns, while many have eyes that are modified into light-emitting organs. The light produced inadvertently by schools of mackerel, in their movements through water teeming with phosphorescent animals, redounds to the benefit of the fishermen. The pale phosphoric cloud, seen from the top masthead, resting upon the surface of the ocean, tells the secret of their exact situation; and, by surrounding it with the great net, large schools are often caught.

Among the insects we have definite experiments to show that the light they emit is a signal; in other words, the insects recognize the lights of their friends. A French naturalist one evening held from his window a living specimen of Lampyris noctiluca (Plate IX.) in the presence of several friends; and a few moments later a companion insect left the gleaming throng without, and alighted upon his hand, touching the captive, whose light was almost immediately extinguished.

M. Raphael Dubois, member of the Zoölogical Society of France, etc., has shown that the Pyrophorus (Plate XI.) uses its light as we would a lantern in the night. When he covered the light upon one side of the insect, it pursued a curved course; and, when both lights were extinguished, it was obviously at fault, and moved along with great care, and was evidently unfitted for nocturnal life.

We have seen how these insects were the means of saving the life of Jaeger, in lighting him out of the forests of the southern islands; how natives attach them to their feet, and employ them as lanterns; while others in South America form an article of trade, being utilized by the ladies as articles of personal adornment.

It must be evident to my young readers, that a practical application of the general features of phosphorescence would be extremely valuable, and in the previous chapter luminous paints and writing fluids have been referred to. An English chemist, named Balmain, has produced from Canton’s phosphorus a paint which is luminous in the dark, and which has been applied to many purposes. Years ago the Chinese used a luminous paint made from powdered mussel-shells. The Emperor Tai Tsung, who reigned in the latter part of the tenth century, possessed a painting which, if examined by day, represented a cow browsing in an open pasture, but if this picture was taken into a darkened room, or looked at by night, the cow was seen to be lying down behind a fence, securely housed and protected. The secret was, that the fence and the cow in the night picture were painted in “South Sea pearl paste,” as the Chinese called their phosphorescent paint, and were alone visible; while in the daylight the painting of “powdered reef-stone” only was seen, representing the animal in a standing position.

To Balmain, however, is due the credit of introducing luminous paint in this country and Europe, and it is applied to many objects. We have the faces of our clocks and watches luminous, so that the time can be told in the dark. Match-safes are rendered conspicuous by the same means, and various other articles.

Through the courtesy of Messrs. Devoe & Co., of New York, I was enabled to examine the application of this paint upon statuary and other objects. Upon entering a dark room, a statue was seen outlined in a wonderful bluish light of remarkable softness and beauty. An arm resting upon a table was vividly luminous, and presented a ghostly appearance. A large globe which hung from the ceiling gave out a soft radiance, quite sufficient to dispel the darkness, and the entire exhibition was suggestive of the varied uses to which the light could be put. Among these might be mentioned the painting of houses, so that they will render the streets luminous; buoys at sea; even the hulls of ships and their sails might be made conspicuous in this way. In London the harnesses of horses engaged in night work have been rendered luminous by this paint; and its availability in mines, and in large sewers like those of London, tunnels, and other subterranean works can hardly be estimated. Artificial fishes are painted, and used as luminous bait; and toys innumerable are placed upon the market, made interesting by application of this discovery.

It is obvious that luminous paint cannot be used in some cases, and to take its place Messrs. W. C. Home and E. Ormerod of London have recently invented a method of utilizing the luminous powder prepared mainly as a sulphide of calcium, for admixture with cements, plaster of Paris, and concrete, the object being to prepare the articles with a self-contained phosphorescent property instead of coating them with luminous paint. They take the proper proportion of any suitable cement, with the right amount of the luminous powder, mixing these with water, and moulding it to the required shape in the usual way, after which it is laid on the ceilings or walls with a trowel. The patentees attach importance to placing the moulded articles, as soon as dry, in a bath of paraffine wax and benzoline, or other water-proofing substance equally good.

In the case of using the luminous cement upon a wall or ceiling, they sponge or brush the surface over with a solution of paraffine wax and benzoline, or other suitable damp-proofing solution. The uses of a luminous cement are manifold; e.g., for the garden, luminous concrete as edging to garden-paths and carriage-drives; for guides and beacons at the entrance-gates of drives; insides of stables; the base of balustrades, or the entirety of balustrades; for roads, as luminous beacons of corners of dark country lanes, and at the ends of bridges, ends of walls, and curbs of foot-paths; for docks; for edging of piers and wharves; for water-works; for the safety and despatch of night-work by the erection of luminous guides and beacons; and for fire-plug notices on walls; in short, for any place where the light of day will sufficiently excite the phosphorescent property as to render the cement or concrete work luminous by night. The difficulty of sighting rifles in the dark has been ingeniously overcome by the use of luminous paint, and it is thought that the armies of various nations will adopt phosphorescent sights for general use.

I have before me as I write, through the courtesy of M. Raphael Dubois of Paris, a fine photograph of a bust of Claude Bernard, taken by the light of numbers of phosphorescent insects (elaters), which shows the possibility of work in this direction.

M. Ch. V. Zenger of Paris has made some interesting experiments, and expressed the belief, some time in 1883, that Mount Blanc could be photographed by phosphorescent light emitted, and I understand this has been accomplished. M. Zenger has photographed objects by the light of Balmain’s phosphoric plates. From a personal communication from this scientist, I will quote some things which he has kindly submitted for the author’s use in this volume, referring to this work and the use of Balmain’s liquid phosphorus. As a light, he says, “No doubt there may exist better and more perfect phosphorescent bodies of green, greenish blue, and violet hue, than are at my disposal; and to avoid the use of sulphurets and sulphides, etc., and to obtain as long a phosphorescence as possible, is all I want to reduce stellar photography to the simplest and cheapest apparatus, and make it available to every one.”

As we have seen, the light emitted by animals, plants, and minerals, of whatever cause, presents much that is mysterious; and the problem of animal phosphorescence would seem no nearer being solved to-day than it was fifty years ago. This is perhaps due to a lack of study and investigation. A glance at the appended bibliography shows that much has been written upon the subject; but it is only within the last decade that serious work in this direction has been done, typified in the superb work of Dubois, and the papers and monographs of the other scientists mentioned. The naturalists of the “Albatross,” the government exploring steamer, are to make investigations regarding the luminosity of the Pacific, during the forthcoming tour on the western coast. The French Academy of Sciences offers this year a prize of three thousand francs for the best paper upon animal phosphorescence. From this it would appear evident that the phenomenon is creating renewed or increasing interest, and in the following years will be the subject of much study and investigation; and we may expect in the near future to have not only its cause explained, but possibly to see a practical application of its possibilities to the wants of mankind.