Nichols.] 
68 
[October 6, 
temperature of the water may differ to a marked extent front that 
of the open pond, especially in summer, and in winter ice may 
form in such a locality while the water outside is much warmer. 
I have myself observed an instance of a pond, 1 in which the water 
was in places nearly fifty feet deep, but where there was consider- 
able shallow water, where, although there was much ice on the 
borders of the pond, the mass of the water was about 4° C. The 
observations were as follows : 
Depth. 
Temperature. 
• 
Surface. 
8°. 9. 
Open pond. 
12 feet. 
4° 
At bottom, under the ice. 
25 feet. 
4°.l. 
Open pond. 
43 feet. 
4°.l. 
At bottom. 
It seems to me that Buchanan’s theory does not suffice by itself 
to cover all cases, but that in small ponds not much stirred by the 
winds it may play an important part. 
Forel, 2 in admitting both the causes already mentioned as con- 
tributing to produce the observed effects, considers the most 
important action to be that of actual conduction, one layer giving 
up heat to another until the surface is reached from which the 
heat is liberated by radiation and by contact with the cooler air. 
I am inclined myself to adopt this view of the matter, and to 
regard conduction as inlaying the most important jmrt, especially 
in large and deep bodies of water. This cause would act compar- 
atively slowly, but it would act regularly and would explain satis- 
factorily the reverse change which takes place in summer where 
in sjiite of the warmer water being at the top, the lower layers 
even to a depth of three hundred meters are warmed up more 
rapidly than they could be by the mere reception of heat from the 
earth. It is to be noticed that in the warm months the maximum 
temperature at considerable dej^tlis seems not to be reached until 
long after the surface temperature has fallen from its maximum. 
To illustrate this statement take Forel’s observations on the Lake 
of Geneva in 1879. 3 
!Lake Konomoc, near New London, Conn., Dec. 20, 1879. 
2 Bibl. Univ., Arch. Sci. (1880), pp. 89-106. 
3 Bibl. Univ., Arch. Sci., Ill (1880), p. 505. 
