556 Proceedings of the Royal Society 
Lomond over a depth of 102 fathoms, or 612 feet, presented in a 
16-inch tube as exactly as possible the same degree of faint yellow- 
ish hue as the water of Loch Katrine. Evaporated to dryness, it 
left a pale, greyish film, amounting to a 33,000th of the water. It 
had only O' 70 degrees of hardness by Clark’s soap- test. Of the 
other liquid reagents, acetate of lead alone caused at once a 
slight haze; oxalate of ammonia and nitrate of silver had at 
first no effect, but in time caused an extremely faint haziness ; 
nitrate of baryta, and ammoniacal phosphate of soda had no effect 
at all. When the water was much concentrated, however, sul- 
phates, carbonates, and chlorides, as well as the bases, lime, soda, 
and magnesia, were clearly indicated by their ordinary tests, exactly 
as in the springs and streams of the adjacent country. 
I examined also the water taken at the same place from the 
bottom at the depth of 102 fathoms. This differed in some 
respects from the surface water directly above it. It contained 
the same salts. Bat nitrate of silver indicated rather less chlo- 
rides; acetate of lead more carbonates; the soap-test denoted a 
trifling additional hardness, namely 0*74 degrees, and the total 
solids amounted to a 28,000th instead of a 33,000th. Farther, 
about the beginning of May, and is more gradual. By filtering a large 
quantity of turbid water, he found the obscuring cause to be a collection of 
amorphous dust, living and dead diatoms, vegetable debris, a few living 
infusoria and crustaceans, and debris of insect larvae and microscopic Crus- 
tacea. They naturally collect slowly in the summer ; but the first cold of 
approaching winter sends them quickly down with the water as it cools. 
In the case of Loch Lomond, these inquiries of Professor Forel would lead 
one to expect little influence from organic or inorganic dust in obscuring 
water where it is so deep as at the places chosen for my observations. Accord- 
ingly, the surface water was remarkably free from turbidity, or deposit on 
standing at rest. But the yellowish colour, faint though it be, constitutes a 
no less powerful obstruction to the penetration of light. The depth of 
colour, and consequently the transparency, vary at different periods, not so 
much with the seasons as with the times of floods. In advanced summer 
and in autumn, the floods increase the colour decidedly, and lessen for a 
time transparency. But my single observation on 6th May, when I found 
the transparency greatest of all a few days after heavy north-east rain, raises 
a question whether floods have the same effect in spring or the end of winter. 
A probable reason for the contrary may be, that the soluble matters of the 
peat-fields and stream-courses, developed by heat, growth, and atmospheric 
action in summer and autumn, are much exhausted by the frequent winter 
floods before the arrival of the floods of spring. 
