230 Wisconsin Academy of Sciences, Arts y and Letters. 
analyses of the water of lakes Amatitlan and Coatepeqne show 
that rather large amounts of this substance are found in them 
and this would reduce materially their capacity for the absorp¬ 
tion of oxygen. With increase in altitude there is a decrease in 
atmospheric pressure; this means a corresponding decrease in 
the tension of the oxygen and the amount absorbed by water will 
be correspondingly smaller. The decrease in the amount of 
oxygen absorbed is about one per cent, for every 82 m. (270 ft.) 
above sea level. 
On this basis the saturation point at the altitude of lake 
Amatitlan is 14.3 per cent, below that at sea level, or 85.7 per 
cent. Since the quantity of oxygen in the upper water amounted 
to about 90 per cent, of saturation at sea level, it was actually 
somewhat above the saturation point for the altitude of the 
lake. The excess was due to the activities of the chlophyll-bear- 
ing organisms which were abundant in the upper strata. 
At the altitude of lake Atitlan the saturation point is only 
about 82 per cent, of that at sea level. But the quantity of 
dissolved oxygen in the upper strata amounted to only 66 to 
69 per cent, which still left a deficiency of 13 to 16 per cent. 
The altitude of lake Ilopango accounts for only 6 per cent, of 
the 16 per cent, deficiency, thus leaving 10 per cent, to be at¬ 
tributed to other factors. In the upper 20 m. of lake Coate- 
peque the quantity of dissolved oxygen was from 15 to 19 per 
cent, below the saturation point at sea level. About 9 per cent, 
of this deficiency can be attributed to the altitude of the lake 
which leaves 6 to 10 per cent, still unaccounted for. 
In the latter part of table II (p. 244) are shown the results 
for dissolved gases which were obtained on two of the Finger 
Lakes in the state of New York. These two bodies of water, 
namely Cayuga and Seneca lakes, belong to the deeper class 
of temperate lakes and they compare very favorably in depth 
with three of these tropical lakes, lake Amatitlan being the ex¬ 
ception. It will be noted that there was a marked difference 
between the temperate and tropical lakes with respect to the 
amount of dissolved oxygen found in their waters. The quan¬ 
tity was distinctly larger in the former than in the latter at all 
depths. The large amount of this gas found in the lower waters 
of the temperate lakes was due to the low temperatures in these 
strata which gave the water a much greater capacity for oxygen. 
At the time of the observations the surface layers of Amatitlan 
