Page:Popular Science Monthly Volume 4.djvu/215

Rh either to mineral particles diffused through the air strata which are traversed by the rain, or to the dejections of certain moths in their last metamorphosis, or to the remains of infusoria carried up by the

winds. But the ignorant multitude continue still to believe in rains of blood, and bow down blindly before so-called miracles which have no existence save in the wild fancies of those who regard them as articles of faith.

We are not concerned now with these errors and superstitions, on which modern science has pronounced its verdict; we propose rather to consider some well-attested facts, the causes of which leave no room for doubt or ambiguity. It is now ascertained beyond question that, where fresh water wears a peculiar tinge, this coloring is due to the presence of infusoria (Euglena viridis, E. sanguinea, Astasia hœmatodes) or to microscopic vegetation (Oscillatoria rubescents, Sphœroplea annulina), or to minute entomostraca (Daphnia pulex, Cyclops quadricornis).

The waters of the sea may also be tinged in a similar way. Thus, in 1820, Scoresby found that the blue or green tinge of the Greenland Sea was caused by an animalcule allied to the medusæ. Of these he counted 64 in a cubic inch; this would be in a cubic foot 110,392, and 23,888,000,000,000 in a cubic mile. According to Arago, the long and sharply-defined streaks of green in the polar seas include myriads of medusæ, whose yellow color, added to the blue of the water, produces green. Off Cape Palmas, on the Guinea coast, Captain Tuckey's ship appeared to be sailing through a milky sea. The cause of the phenomenon was the multitude of animals floating at the surface, and masking the natural tint of the water. The carmine-red streaks which various navigators have sailed through on the high-seas are produced in the