248 THE POPULAR SCIENCE MONTHLY. 



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 col- 

 ored 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 ex- 

 periment 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 dis- 

 tilled water evaporated out of the sea and everywhere, and car- 

 ried on in the form of clouds, and falling in drops even that rain- 

 water 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, par- 

 ticularly 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 com- 

 plex 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 



