48 



BULLETIN OF THE BUREAU OF FISHERIES. 



period is about 28.5° F.," which is the freezing point of sea water. This temperature 

 is perhaps reached at one time or another nearly every winter. 



An analysis of this curve reveals several other facts worthy of mention. (We 

 omit as irrelevant the interesting relations between the cur\-es for air and for water.) 

 There are two comparatively level sections having a duration of about two months 

 each, occurring in midwinter and midsummer, respectively. During each of these 

 periods, the range of temperature is only about 3 degrees. The remainder of the year 

 is made up of the long vernal ascent, and the somewhat more abrupt autumnal decline. 

 During 131 days, or rather more than a third of the entire year (June 3 to Oct. 12), the 

 temperature remains above 60°; from May 5 to November 8, the temperature exceeds 

 50°; while from April 3 to December 5, the curve is above the 40° line. On the other 

 hand, from December 26 to March 14, the temperature of 35° is not exceeded. 



The water here employed was that drawn from the surface at the local pier, close 

 to the buildings of the station. This water rapidly changes with the tides which sweep 

 through Woods Hole Passage, and therefore is not liable to the extreme fluctuations 

 found in more inclosed areas. The figures doubtless represent fairly well the surface 

 (and likev/ise the bottom) temperature of Woods Hole Harbor and of the adjacent 

 shallower parts of Buzzards Bay and Vineyard Sound. The mean water temperature 

 for this entire period of five years was 51.01° F. ; the mean air temperature for the same 

 period was 51.98°. Since th^se figures are based upon temperatures taken at noon, 

 they are doubtless somewhat too high, though the error in the case of the water temper- 

 atures is probably slight. 



It will be important for our future discussion to make a comparison of the water 

 temperatures at Woods Hole and those at the United States Fisheries stations at Glouces- 

 ter, Mass., and Boothbay, Me. For this purpose we have employed the records of 

 only three years at each station, the same years (1905, 1906, 1907) being used in each 

 case. Thus the figures here presented for Woods Hole necessarily differ somewhat 

 from those given in the preceding table. 



T.\BLi3 II. — Mean' \V.\ter Temperatures (Moon) at Boothbay, Gloucester, and Woods Hole 



FOR THE Ye.\rs 1905, 1906, 1907." 



a Based upon records furnished by the superinteudents of these stations, 

 b Based on two years only (1906. 1907), 



From the foregoing figures the following facts may be gathered: 



(i) That the mean water temperature for these three years was highest at Woods 



Hole (50.59°), next highest at Gloucester (47.95°), and lowest at Boothbay (44.44°). 

 (2) That these differences are at a maximum during the summer months, being 



reduced to a minimum or even reversed during the winter months. Thus the annual 



range of temperature is greater as we pass to the southward. 



o Stated as rS* in the table. This was doubtless due to an error in the reading. 



