of Gases found in Stagnant Waters. 181 
ing of the air, rain, and, above all, the presence or absence of the matter 
which gave a green colour to the water, had the effect of considerably 
modifying the results, both as to the quantity and proportion of the gases 
dissolved in the water of the pond. As soon as the green substance re- 
appeared, accompanied with heat and the solar influence, the oxygena- 
tion of the water was considerable 3 it diminished rapidly, on the con- 
trary, in the absence of the sun and heat. 
The author has devoted nearly a whole year to the daily examination 
(noting at the same time all the accessory circumstances) of the gases 
contained in the water of a deep-fish pond, fed by springs and rain, and 
containing about 8000 cubic feet of water. The walls of it were com- 
posed of slate-stones cemented with mortar, and it contained scarcely 
any conferva visible to the naked eye. He has likewise examined the 
water of many other ponds, and also that of the Maine and Loire. These 
experiments were generally made at the same hour, between one and 
three o’clock in the afternoon, although many of them were made at 
other times of the day. Mr Morren gives circumstantial details respect- 
ing the mode of operation which he prefers, the instruments he employed 
to disengage and collect the gases dissolved in the water, and the analytical 
methods he adopted. They are of such a nature as to inspire perfect con= 
fidence in the accuracy of his results. 
His memoir likewise contains a table in which are inserted the propor- 
tions of the gases in the water of the pond, taken day by day for nine 
months, as well as the state of the weather, and the presence or absence 
of the green matter. From his long-continued researches, he thinks him- 
self authorized to draw the following conclusions : — 
The oxygenation of the water is most considcrable in proportion to 
the intensity of the solar light and the elevation of the sun itself. It ne- 
vertheless takes place, though in a smaller degree, under the influence of 
a diffused light. It either ceases altogether, or cannot be appreciated in 
a rainy day. 
It commences at day-break, increases slowly at first, then rapidly, and 
reaches its maximum at four or five o’clock p.m. 
Tn winter, there must be a long succession of fine days before the wa- 
ter attain the same degree of oxygenation as in summer. The variations 
are much more rapid in this latter season, and the quantity of the oxygen 
of the air dissolved in the water, sometimes diminishes so much that cer- 
tain kinds of fishes can no longer live in it. 
The least oxygenated water contained 16 to 17 per cent. of oxygen in 
the dissolved air, and that which was at the maximum contained 61 per 
cent. 
The quantity of azote has varied little, and the carbonic acid seems to 
undergo variations the reverse of those of the oxygen. 
When a black curtain was extended over the whole surface of the 
pond, the oxygenation was seen to diminish rapidly (from 49 to 22 per 
