1875.] 213 [Burbank. 



The pond referred to is known on the town and county maps as 

 Cranberry Pond. On a recent map of Worcester County, it is incor- 

 rectly represented as the source of one of the branches of the Nashua 

 River. In fact, no water flows from it at any season, nor does any 

 stream flow into it. Although its area is small, — only about thirteen 

 acres, its depth in some parts is sixty or seventy feet. It occupies 

 one of the deepest valleys in a mass of glacial drift which covers an 

 area of two or three square miles, and which is very remarkable for 

 its uneven surface, steep slopes, deep hollows and long and narrow 

 ridges. 



The height of the water in the pond varies through a vertical 

 range of about six feet. It is a common saying among the inhabi- 

 tants of the vicinity, that the water is highest in a dry time, and also 

 that it rises and falls regularly once in seven years. These sayings are 

 not altogether without foundation in facts. The water is often higher 

 in dry weather in mid-summer than during the copious rains of the 

 Autumnal Equinox. That there are, also, fluctuations ranging through 

 several years, is illustrated by the following facts, observed about the 

 year 1852. 



For several years the water had been quite low, and a dense 

 growth of Pitch Pine (Pinus rigidd) had grown up along the margin, 

 near the water. After these pines had attained about seven years' 

 growth, the water rose several feet, and stood above their roots dur- 

 ing at least one whole season, and until the trees were all killed by 

 the moisture. 



It is not necessary to seek an explanation of these facts in the pop- 

 ular notion that the pond is fed entirely by springs at its bottom, or 

 has a hidden outlet by which its waters are discharged at intervals. 

 The height of the water is undoubtedly regulated by the combined 

 effects of the rainfall and evaporation. 



The inference is obvious that careful measurements and records of 

 the varying height of the water in such ponds throughout the State, 

 continued for a series of years, would aid in the solution of several 

 important questions relating to our climate. 



1. The ratio of evaporation to rain-fall may be determined. 



2. The question whether our climate is gradually growing dryer 

 may be solved. 



3. The effects of forests upon precipitation and evaporation may be 

 studied by the aid of observations made upon such ponds when sur- 

 rounded by woodland, and afterwards, when the forests have been 

 cleared away. 



