Nichols.] 
60 
[October 6, 
While different ponds thus vary from each other, the tem- 
perature of the same pond at the same time in different years 
varies likewise. Thus Table IV contains the record of tempera- 
Table IV. Observations on Fresh Pond. 
U g 
•4-3 D 
Temperature in centigrade degrees. 
Date. * 
I Height of Wa 
above 
Cambridge Dat 
Two feet 
from surface. 
Eighteen feet 
from surface. 
Thirty-five feet, 
more or less, 
from surface. 
Feet. 
o 
o 
o 
July 16, 1878 . . . 
14.60 
25.3 
16.8 
9.6 
July 16, 1879 . . . 
14.57 
27.2 
17.0 
11.0 
August 20, 1878 . . . 
14.67 
24.0 
20.0 
10.2 
August 19, 1879 . . . 
14.17 
21.2 
20.8 
11.0 
January 2, 18 79* . . 
14.78 
0.5 
1.0 
1.0 
January 5, 1880* . . 
11.93 
2.0 
2.3 
2.7 
January 22, 1879* . . 
14.58 
0.9 
2.0 
1.8 
January26, 1880* . . 
12.00 
2.8 
3.0 
3.2 
* Taken through the ice. 
ture observations in Fresh Pond at corresponding times of two 
successive years. The difference detween January, 1879, and Jan- 
uary, 1880, is very marked, and this might be ascribed to the char- 
acter of the season. Thus the monthly mean temperatures as 
observed at the U. S. Signal Office in Boston were, in Fahrenheit 
degrees, as follows : 
1878. 
1879. 
October, 
55°.3 
56°.6 
November, . 
39°. 9 
39°. 2 
December, . 
29°. 6 
32°. 6 
1879. 
1880. 
J anuary, 
24°.5 
35°. 0 
Mean for four months, 
37°.3 
40°. 8 
Difference, 3°.5 F. = : 
1°.95 C. 
