479 
of Edinburgh, Session 1881-82. 
In the beginning of autumn the sea off the west coast of Scotland, 
near the village of Ballantrae, and also in Brodick Bay, was visited, 
and the waters examined by means of submerged coloured surfaces, 
and by means of the spectroscope. The water was here found to be 
much greener than any previously examined. A large quantity of 
this water was filtered, when it was found that most of the suspended 
particles were fine grains of sand. From this it is concluded that 
the greenness of our northern seas is in part due to the reflecting 
particles being yellow, and the reflected light, therefore, deficient in 
the more refrangible rays. These yellow sand particles not only 
explain part of the greenness of our northern seas, but they also 
explain their comparative darkness and deadness, the yellow sand 
particles reflecting so little light. The importance, however, of even 
these bad reflectors was very evident during the time the observa- 
tions were being made. It was noticed that the water was much 
more brilliantly green during and immediately after an inshore 
wind, and when the filter showed the water to have a good deal of 
sand in suspension, than after a calm, when many of the particles 
had settled out. Some water collected about a mile seaward from 
Ballantrae was examined in a glass tube 7J m. long, and was found 
to be of a blue green colour. 
The water of Loch Lomond was next examined, and found to be 
a perfect contrast to any previously described, being of a colour 
nearly complementary to that of the Lake of Geneva. A white 
surface seen through its waters appearing yellow, and the submerged 
coloured surfaces showed its waters to have their greatest absorption 
for the rays of the violet end of the spectrum. Its waters reflect a 
slightly yellowish light, its spectrum being brightest in the yellow. 
This water is so deficient in reflecting particles that its brightness is 
never greater than what we call brown. If it was supplied with 
abundance of reflecting particles Loch Lomond would be a yellow 
lake. 
Well waters were also examined for colour by placing them in 
long tubes, and looking through the water at white and at coloured 
surfaces. The tubes were in pieces, so that they could be fitted up 
in lengths of from 3 m. to 15 m., to suit the transparency of the 
water under examination. The tubes were fixed horizontally, and 
at a convenient height for looking through them, and the water to 
