of Edinburgh, Session 1881 - 82 . 
477 
distance under the water, and seen through the empty tube, being 
the same, whether the surface was turned towards the sun or away 
from it. It was also shown by the fact that at a depth of 6 m. 
these solid particles were found to reflect about as much light as 
a white surface did. These solid particles act like a fog, and, while 
they stop the light penetrating in a direct line, yet allow it to 
penetrate much further by internal reflection. The sun’s rays get 
entangled — so to speak- — among the particles, and are reflected from 
particle to particle, becoming a deeper blue with each reflection, so 
that the particles become illuminated with blue light. From this 
it is obvious that the more transparent the water, and the greater 
the reflecting power of the particles, the more deeply coloured will 
the water appear. 
The Lake of Como was the next water visited. A white surface 
seen through its waters, showed it to be as deeply coloured as the 
Mediterranean, yet the absence of white reflecting particles in its 
waters and its dark-coloured bottom, cause it to appear compara- 
tively dark and colourless. When a quantity of white reflecting 
particles was artificially mixed up with the water in this lake a fine 
blue-green cloud was formed, which remained visible for some time 
amidst the darker waters, and showed that all this lake required to 
make it brilliantly coloured was the presence of white suspended 
particles in its waters. The waters of Como, in their passage from 
the lake to form the river Adda, change to a fine blue. This 
sudden alteration in the appearance of the water is shown to be 
probably due to the addition of fine reflecting particles to the 
water on entering the river. 
Lago Maggiore, compared with Como and the Mediterranean, 
looks greener than either, but reflects more light than Como. 
The Lake of Geneva, whose waters have been so highly praised by 
all writers, was next visited, and the explanation given of the 
colouring of the Mediterranean was found to apply here also. 
Near Bouveret, where the Rhone enters the lake, all the variety of 
colour phenomena seen in the Mediterranean were repeated. The 
light coloured muddy waters of the entering river, as they stretched 
far into the lake, represented the whitish waters near shore in the 
Mediterranean, and where this whitish stream mixed with the 
waters of the lake, the bright blue-green of the Mediterranean was 
