Page:Popular Science Monthly Volume 41.djvu/260

248 church-steeple, and deeper—that it reaches from here up into Salvan and down to Vernayaz. Then you would see the water from above it all blue."

"Is the lake, then, really so deep? "

"Yes, and deeper."

I will not continue the conversation any longer. It went on with various simple experiments, beginning with differently colored stones, which I let drop into the water, and then placed on the white, then with setting the glass with its weakly bluish contents on differently colored papers, and ended with my trying to make the children perceive how the colors changed when they were seen through the whole depth of the glass. I will not say that the little ones were brought to a full comprehension of the matter; but they stuck fast to the assertion that water is blue, of an infinitely weak blue, and that the blue color can not be seen till one looks into a certain depth of it.

Physicists first acquired this knowledge by means of an experiment of Bunsen's, who let a piece of white porcelain fall into a tube filled with distilled water, and satisfied himself that the descending piece looked bluer as it sank deeper. Bunsen had, of course, provided that only white light reflected from the ceiling of his room should fall into the tube, and not the blue light of the sky. The experiment has been modified in various ways, and made more convenient, but has always given the same result; and it is now established as a scientific truth that chemically pure water, free from all other constituents, either dissolved or floating, has a bright, clear, blue color.

But there is no such water in Nature, for rain-water, even distilled—water evaporated out of the sea and everywhere, and carried on in the form of clouds, and falling in drops—even that rainwater contains some dissolved substances, and still more of little microscopic bodies that are floating in the air which the drop carries with it in its fall.

Yet we can assure ourselves at least as to the dissolved salts, in which sea-water, for example, is rich, that they are all, particularly common salt, colorless in the crystalline condition, and therefore have not the least influence on the color of sea-water. Seamen and sailors, although uninstructed in this matter, and without knowledge, know very well that they, going away from the coast, in a short time reach the clear, the "blue water," and then sail over deeps till they can not reach the bottom with their anchors.

I have already said that every phenomenon in Nature is a complex affair, and depends on many causes and conditions. This is true of the coloring of large masses of water, as of lakes and seas, which are indeed, as is known, of very different shades. It