Page:Popular Science Monthly Volume 17.djvu/725

Rh waters near Madeira had a peculiar obscurity, which was occasioned by numerous minute tufts of oscillatoria waving in the mass. These plants were found all the way to the West Indies, sometimes thick enough to give a color to the water, but never wholly wanting. In other cases the sea is colored red by animals of different kinds, by minute crustaceans or infusoriæ, or eggs. The name of Red Sea or Vermilion Sea has been given to two different phenomena in the Gulf of California, in which the water is colored two distinct shades of red by different microscopic infusoriæ. One of the coloring animals is irritating to the skin, and produces blisters and sores on the bodies of those who come in contact with it. Diatoms often give rise to similar colorings. Professor Cleve, of Upsala, mentions fifty-four species of diatoms which have been found on the surface of the Sea of Java, and speaks of others which have been observed between Europe and Greenland and in Davis Strait. Grunow gives a list of thirteen species which are found near the Nicobar Islands. Kjellmann gives especial attention to the diatomaceous flora in his treatise on the alga of the Kara Sea. The Swedish polar expedition of 1872-'73 saw on the northwestern coast of Spitzbergen an expanse of sea of considerable extent covered with masses of diatoms of a single species, forming what the English sailors call a "sawdust sea." The same has been observed in Davis Strait, in the Kara Sea, and on the northern coast of Finland, covering large spaces. Johann Steenstrup found spots in the Atlantic Ocean between Scotland and Greenland, where the water changes from ultramarine to an emerald green, so suddenly that only a line separates the two colors. The coloring seems to have some relation to temperature, the green prevailing in the warmer months, the blue in the colder, and is thought to be connected with the development of diatoms. Professor Ossian Sars, of Norway, has observed a dull grayish-green color of the sea, which he ascribes to a bathybius that he found floating on the surface of the water. Similar colorings occur in fresh water, and have received the names at times of bloody rains, bloody dews, etc. Schwammerdam, observing water thus strangely colored at Vincennes, was strongly affected by the sight, but, examining it, found that the color was given by small crustaceans. The Husten Lake in Switzerland has been colored by oscillatoria which were so thick in the water as to make it unhealthy for the fish, and to cause them to die; the fishermen are well acquainted with the phenomena, and speak—referring to the mixture of green and red—of the lake blooming. The water in one of the lakes of Denmark has been found colored a deep red by another oscillatoria. In still other cases the colors are given by the spores of an alga. The so-called "bloody rain" is colored by an alga, which, because they have not noticed it before, some believe to have come down from the clouds, while others think it was previously present but was dried up, and has only been refreshed and enlivened by the rain. It has recently been identified with the "red snow," a one-celled, spherical plant, green or red in color, which may be increased by division, and is propagated rapidly in water or melting snow. In the still waters of the coast of Denmark a red deposit appears on the decaying sea-weeds, or floats loosely on the surface, giving a raspberry-red color to the water. It is caused by bacteria, which, probably contributing to the decay of the sea-weed, are thought to have a part in the formation of the sulphuretted hydrogen gas so common in that region. Of a similar character—caused by vegetable or animal growths, often by bacteria—are the colored spots which appear on decaying food; and it can no longer be considered an occasion of marvel that a pond becomes as red as blood, or that what seem to be drops of blood may appear on the sacramental wafers. These phenomena are all assignable to natural causes which have been traced out and are clearly known.

Luminous Paint.—The invention of luminous paint is based upon the fact that certain substances after having been exposed to the light will continue to shine for some time after the light is removed. The existence of this power in some gems has been known for a long time, and is mentioned in some of the works of the ancients. Japanese antiquaries tell of a luminous stone that was dug out of the ground in 669.