254 
SCENERY OF SWITZERLAND. 
in water, thus obtaining a yellow solution. By adding 
a small quantity of this to the blue water of the 
Lake of Geneva, he was able to obtain a green 
colour, exactly similar to that of the Lake of Lucerne. 
He refers as a test case to the sister Lakes of 
Achensee and Tegernsee in the Tyrol. The basin 
of the Achensee is free from peat, in that of the 
Tegernsee peat mosses cover a large space. The 
former is a brilliant blue, the latter a lovely green. 
He concludes, therefore, with Wettstein, that the 
bluest lakes are those which are the purest; while 
green lakes contain also a minute quantity of vege- 
table matter, or peat, in solution. 
This is, however, by no means the only cause to 
which water owes a green hue. Shallow water over 
yellowish sand is green by the reflection of the yellow 
light from the bottom. Again, after storms the water 
is often rendered thick and turbid. After the 
coarser mud has subsided the finer impalpable 
particles give the water a greenish hue, which, how- 
ever, is only temporary, though it may last for some 
time. Finally, the water is sometimes coloured green 
in patches by microscopic algae. 
But though the blueness of lakes and seas is not 
owing to reflection from the blue sky, the brilliancy, 
beauty, and variety of tone and tints, the play of 
