Page:Popular Science Monthly Volume 38.djvu/234

222 hardly take any fish, at least in the daytime, if they could see as far as we see in the air.

The color of water varies from blue to greenish, usually according to the degree of its clearness. Objects at twenty metres' depth begin to take a bluish hue, and at from twenty-five to thirty metres the light is so blue that dark-red animals look black, while green and bluish sea-weeds seem almost white by contrast. Coming back quickly into the air, eyes accustomed to the blue light see the air-landscape red. The red rays are extinguished first, a fact which had been already demonstrated by laboratory experiments. The blue rays, being absorbed in a less degree, penetrate farther; and these are the rays which act most energetically on the photographic plate. This fact disposes of the objections which some students have repeated with a persistency that is not creditable to their ideas of physics, against the use of photographic plates in determining the depth to which daylight can penetrate through water.

When there is a swell, the diver's task is a hard one. He is constantly tossed about in spite of himself, and an irresistible force compels him to swing like a pendulum. This oscillation of the water, which is a counterpart of the waves of the surface, is nearly as perceptible at thirty metres as at ten metres. It can not be a surf phenomenon, for fishermen find that, after a storm, depths of fifty metres and more are swept by it. Special apparatus and experiments are required to determine to what depth it extends; but, in view of the incompressibility of water, I should not be astonished to find it extending very far down. In this matter, as well as in a great many others, the diver is in a condition to gain valuable information by which new avenues may be opened for the study of the phenomena of Nature.—Translated for The Popular Science Monthly from the Revue Scientifique.



HE people who live on the extreme northwest corner of our continent are far from being an ugly or an ill-made race. Though they are not tall—a man of five feet ten inches is a tall man among them—they are well-proportioned, broad-shouldered, and deep-chested. The men, as a rule, are particularly well "set up," like well-drilled soldiers, and walk and stand with a great deal of grace and dignity. I fancy that a good deal of the erect carriage of the men comes from their habit of carrying the gun,