Nichols.] 
54 
[October 6, 
The points on which I particularly desired information were : — 
(1) the difference in temperature at different seasons between the 
top and bottom water of the various ponds, (2) the rate and man- 
ner of the progressive cooling of the water in the fall and of the 
warming up in the spring, and (3) the extent to which the tem- 
perature is lowered in winter. 
The first pond chosen for examination was Fresh Pond. This 
pond covers an area of some two hundred acres, and serves as the 
source of water-supply of Cambridge, Mass. It is fed mainly by 
the ground-water or by actual springs. The present observations 
were made at the entrance to the bay from which there is pumped, 
for city supply, from two and a quarter to two and a half million 
gallons per day on the average. The water at this part of the 
pond is, as a rule, from thirty-five to forty feet deep. The obser- 
vations were made at three depths; one as near the bottom as 
possible, one at twenty feet from the surface, and one at two feet 
from the surface ; no great stress is laid, however, upon the latter 
observation, as the surface temperature may, in the case of a small 
pond, vary to the extent of several degrees, during the same day,* 
and at different points on the pond. The results are presented in 
the table on the opposite page. 1 (Table I.) 
Another pond on which more or less frequent observations of 
temperature have been made, is Mystic Pond, from which a por- 
tion of the City of Boston is supplied. Mystic Pond (or Lake) 
covers in all a flowage area of some two hundred and thirty acres 
and derives a considerable portion of its supply from surface 
water, namely from the Abajonna River. The deeper portion of 
the pond — the original pond, in fact — forms a basin of from 
one hundred to one hundred and twenty-five acres extent and is, 
in some places, of considerable depth. The point at which the 
observations were made was well out into the ]iond, say one 
thousand feet from the shore and about one-half a mile from the 
1 These observations in Fresh Pond, in connection with the results of chemical exam- 
inations, were presented at the Saratoga meeting of the American Association for the 
Advancement of Science, August, 1879, and published in the First Annual Report of 
the Mass. State Board of Health (1880), pp. 97-107. As the Board of Health Reports 
have a limited circulation among other than sanitarians, I have taken the liberty of 
communicating the results to this Society. 
