THE COLORS OF WATER. 



251 



Blue water also takes on another tint when objects lying on the 

 ground are seen through it, and this mixed color tone depends on 

 the color of the ground. We can easily verify this by the simple 

 experiments described above with blue colored water in a cylinder 

 glass. White bodies, pieces of porcelain for instance, appear light- 

 blue, yellow-green, red- violet, and, the deeper they sink, the more 

 is this shading from blue washed out, till it is destroyed. The 

 red shades vanish first of all. 



The depth to which no trace of bottom-colors reaches us is cer- 

 tainly not little, and may, under favorable conditions, be esti- 

 mated at several hundred metres. But the question is a large 

 one, and we will consider a little more carefully to what extent 

 the more or less favorable conditions I have mentioned have been 

 determined. 



I have already said that pure water does not exist in Nature. 

 It always must contain dissolved or floating substances which 

 will change its colors. Peat waters contain brown and blackish 

 organic matters in solution. They may be perfectly clear and 

 transparent, but the colors which the humus acids and similar 

 substances lend them will always produce a certain effect upon 

 them, which will be re-enforced by the dark-brown or black colors 

 of the bottom of the peat lakes. It has also been observed that 

 filtered water from a blue lake on evaporation leaves a white or 

 light gray, and that from green lakes a yellow sediment ; and that 

 thus blue lakes contain white matters and green lakes yellow ones 

 in solution, whose colors produce with those of the water mixed 

 tints. The difference in the colors of the Lake of Geneva and 

 of the Bodensee is explained on this principle, but the results of 

 the experiments on which the conclusion rests have been dis- 

 puted, and there is much room for doubt on the subject. What- 

 ever may be thought of this, it is certain that no water in Nature 

 is perfectly clear and transparent, but is more or less turbid by 

 the presence of other substances floating in it. That this turbidity 

 is of greater or less importance, that we can distinguish at greater 

 or less depths objects swimming in the water, like fishes, or lying 

 on the bottom, are taught by daily experience as well as by ex- 

 periments which have been made by sinking solid bodies in sun- 

 light and on cloudy days and at different seasons, or by letting 

 down sources of light, such as burning lamps and incandescent 

 electric lights, and ascertaining the depth at which a perceptible 

 glimpse of them can be obtained. It is to be regretted that these 

 as well as other experiments upon the penetrating power of light 

 have been made only in waters not quite clear, as in a few Swiss 

 lakes and the Mediterranean Sea. Whoever has traveled on the 

 coasts of Norway must have been astonished at the transparency 

 of the water in many of the fiords ; it is also affirmed that in some 



