PHYSICAL OCEANOGBAPHY OF THE GULF OF MAINE 



557 



In 1915 a west-east gradation in surface temperature was recorded along 

 the coast of Maine from May 10 to 14, from 7.8° near the Isles of Shoals and off 

 Casco Bay to 5° off Penobscot Bay and 4.2° to 4.8° near Mount Desert Island. No 

 doubt the precise readings vary with the state of the weather, however, as well as 

 with the date and exact locality and from year to year. I must also caution the 

 reader that at this season the surface temperature is changing so rapidly in the west- 

 ern side of the gulf that a difference of a few days, one way or another, will make a 

 considerable difference in the readings obtained; less so in the eastern side. 



Although the precise surface temperatures at any given date vary from one May 

 to the next, depending largely on the forwardness of the season on the land, probably 



Fig. 27.— Surface temperature, first balf of May, 1915 



the comparative rates of vernal warming do not vary widely from year to year in 

 different parts of the gulf. 



It appears from combining the records for the three years 1913, 1915, and 1920, 

 that this change is most rapid in the inner part of Massachusetts Bay, where the 

 surface warmed from 3.05° on April 6 (station 20089) to 8.89° on May 16 (station 

 20123) in 1920. Similarly, temperatures taken by the Fish Hawk in 1925 show the 

 surface of the southern side of the bay, generally, warming from 5.3° to 6.8° on 

 April 21 to 23, to 7° to 11° on May 20 to 22. 



At the mouth of the bay, where the surface does not chill to so low a figure at 

 the end of the winter, a less rapid rate of vernal warming causes about the same 



