556 
BUIylvETlN OF THE BUREAU OF FISHERIES. 
lake and the several products are added, the result will show the mean temperature 
of the water. This is shown by the following example : 
Table V. — Method of Computing Mean Temperature of Lake: Canandaigua Lake, August 
20, igio. 
Depth in 
meters. 
Temper- 
ature. 
Volume. 
Product. 
o-io 
21.30 
Per cent . 
0. 221 
4. 707 
10-20 
14. so 
. 184 
2.668 
20-30 
7.40 
.165 
1. 221 
30-40 
6.25 
.147 
.907 
40-50 
S -85 
. 126 
•737 
50-60 
5- 75 
.094 
•540 
60-70 
5-65 
,049 
.277 
70-84 
5-45 
.014 
.076 
Mean temperature (Tm®) = 
II- 13 
These results are, of course, accurate in proportion as the temperatures recorded 
give a fair picture of the mean temperature of the several strata and in proportion as 
the hydrographic survey gives a correct account of the volume of the lake. Extreme 
accuracy can not be claimed in this case for either factor, but the results are approxi- 
mately correct. 
The question has been recently raised, whether a single series of temperatures can 
give a correct idea of the mean temperature of the water of the entire lake. In a 
recent review Halbfass® states that the presence of the temperature seiche makes clear 
“die Bedeutungslosigkeit einer Beobachtungsserie in vertikaler Richtung in einem 
vereinzeltem Punkt eines Sees.” This statement is entirely too strong, according to 
my obseiA^ations, and, indeed, Halbfass in a later paper modifies the statement. No 
one in recent years would have believed that a single set of observations, or even 
numerous sets, made at one end of a lake would show the mean temperature of the 
water, least of all would such a series be trusted if taken during a windy period. This 
was true long before the temperature seiche was known. Our recent knowledge of the 
temperature seiche shows that conditions similar to those called out directly by wind 
may exist at almost any time on account of the oscillations following the influence of 
winds; hence comes need for increased caution; but it is by no means clear that a single 
series of temperatures taken under ordinary weather conditions, at or near the center 
of oscillation of a lake, are “without significance.” No one would claim minute accu- 
racy for a result based on such a series; but there is as much reason as ever to believe 
that from such a series there can be derived a temperature for the water of the lake, 
which though not minutely exact, is approximately correct — close enough for all pur- 
poses of a general discussion. The result is of the right order of magnitude, as the 
following instances show. 
We can not find that many observers have taken series of temperatures with a 
view of testing the accuracy of results derived from a single series near the middle of 
® Halbfass, W.: Internationale Revite der gesamten Hydrobiologie und Hydrographie, vol. v, 1912, p. 471, Jan., 1913. 
