PHYSICAL OCEANOGRAPHY OF THE GULF OF MAINE 
841 
Evaporation, of course, partially offsets precipitation. Unfortunately, no data 
are available on this subject from any localities that might be supposed to approxi- 
mate conditions as they prevail at sea in the Gulf of Maine; the outer islands, for 
example, would be such. Nevertheless, there is no reason to suppose that evapora- 
tion at sea is greater than on land, especially when the sea is blanketed with thick 
fog, as the northern and northeastern parts of the gulf and its offshore banks often 
are during the summer season. The following records of evaporation for Maine, 
Massachusetts, and Nova Scotia may therefore be taken as the maximum. The 
average monthly evaporation from a free water surface at three stations in Maine 
in the basins of the Penobscot, Kennebec, and Androscoggin Rivers is given by 
Barrows (1907a, p. 114) as follows, in inches: 
Month 
Average 
evapora- 
tion, in 
inches 
Month 
Average 
evapora- 
tien, in 
inches 
March 
2. 23 
July 
5. 28 
April 
3. 48 
August 
5. 12 
1.90 
September 
3. 00 
June 
2. 87 
October 
2.33 
No data are available for the winter months, when the observations were neces- 
sarily made from a frozen surface, but it may be assumed that evaporation takes 
place no more rapidly from open water from November through February than in 
October or March — say at the rate of about 2.2 inches monthly. This suggests a total 
evaporation for the year of about 35 inches of fresh water. 37 According to Fitz- 
Gerald (1886), the annual evaporation is somewhat larger near Boston (about 39 
inches), as might be expected. 
Data supplied by the United States Weather Bureau for Yarmouth, Nova 
Scotia, more closely paralleling conditions over the gulf because of the greater fre- 
quence there of onshore winds, show the following monthly averages over a period 
of 13 years: 
Evaporation at Yarmouth, Nova Scotia 
Month 
Average 
evapora- 
tion, in 
inches 
Month 
Average 
evapora- 
tion, in 
inches 
April 1 
1.08 
August 
3. 55 
3. 57 
1.59 
May 
3. 04 
September _ 
June 
3. 49 
October 
3. 94 
1 1920 only; ice in the tank on several days. 
Assuming an average evaporation of 1.5 to 2 inches monthly, for the period 
November to March, the annual evaporation of fresh water at Yarmouth would be 
close to 29 inches from a surface of open (not frozen) water; the average for the Gulf 
of Maine is probably not more than 30 inches. These measurements are for fresh 
87 These measurements were taken freely exposed to the sky (Barrows, 1907a, p. in, pi. 21). 
