Page:Popular Science Monthly Volume 26.djvu/557

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541
WHY BIRDS SING.

water, and not an abandoned lagoon of the Red Sea. By chemical and spectral analysis, it contains neither iodine nor silver, nor lithine, while all those substances are found in the Arabian Gulf, a body whose waters differ from those of the oceans only by their greater density consequent on the strong evaporation to which they are subjected.

The determination of the air dissolved in the ocean is attended with many difficulties. We can only indicate a few prominent principles. This air has not the same composition as the air we breathe, although it differs but little in that respect from the air held in springs and rivers. Oxygen, which forms only a fifth of the atmospheric air, being more soluble in water than nitrogen, constitutes about one third of the air which is expelled from water by boiling. The volume of gas absorbable by water diminishes as the temperature rises. Cold water is richer in air than warm. Moreover, the law of decrease being regular for nitrogen, while it is less simple for oxygen, the relative proportions of the two elements are variable in waters of different temperatures. According to Mr. Tornöe, there is a little more oxygen at the surface than theory calls for, while in the zones where animal life is largely developed there is a slight deficiency. The presence of sunlight, or the cutting of it off by clouds, has no important effect; and the same may be said of the enormous pressures to which deep-sea waters are subjected. But little carbonic acid occurs dissolved in a free state, although that gas is very abundant in combination. Mr. Tornõe, who has given this subject careful attention, thinks the older chemists collected carbonic-acid products of the decomposition of carbonates or bicarbonates at the boiling-point He finds an alkaline reaction in sea-water, which he attributes to a small quantity of free salts of soda. Mr. Hamberg, a Swedish chemist, who has recently studied the waters of the Greenland seas, agrees with Mr. Schloesing that marine water contains neutral carbonates, bicarbonates, and slight traces of free carbonic acid, and that temperature and atmospheric pressure have a complex influence on both the uncombined gas and that which is united to bases.—Translated for the Popular Science Monthly from the Revue des Deux Mondes.


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WHY BIRDS SING.

By Dr. B. PLACZEK.

I HAVE long been an interested observer of bird-life. The situation of my house and garden, on the terrace-slopes of the Spielberg, affords me favorable opportunities for studying the habits of the feathered tribes. They build their nests in my garden, and lend themselves with great docility to the purposes of the friendly spectator of their movements. At one time the nest of a hedge-sparrow (Sylvia