670 BULLETIN OF THE BUREAU OF FISHERIES 



The hourly temperatures taken on our summer cruises have not yet been stud- 

 ied in detail, but prehminary examination shows that the spread between aii' and 

 water continues of about this same order of magnitude over the open gulf from May 

 until July, averaging about 0.3° to 5°. 



Usually we have found the air at least 2° but seldom as much as 4° warmer 

 than the water of the open gulf in August and September by day. This accords 

 with Craigie and Chase's (1918, p. 130) and with Craigie's (1916a) records of air 2.2° 

 to 6.24° warmer than surface over the Bay of Fundy generally during July, 1915, and 

 ail' 2° to 3.8° warmer than water along a section of the bay from Grand Manan to 

 Nova Scotia on August 27 to 29, 1914. Mavor's (1923) experience was also similar. 

 (No night time records have been published for the Bay of Fundy.) 



The only regional distinctions that I dare draw in this respect for the open gulf 

 until the very considerable mass of material is more carefully analyzed, is that the 

 difference between daytime temperatures of the air and of the water averages great- 

 est near the shore, as was to be expected. 



It is common knowledge that the air along our seaboard is often much warmer 

 than the water that actually washes the coast during the warmest part of the sum- 

 mer. Thus, we find the air averaging 6° to 7° warmer than the water at Boothbay 

 and Gloucester and in Lubec Channel about July 25, 1920 (figs. 29 to 31), with 

 differences as wide as 10° C. (18° F.) on individual hot days. 



Vachon (1918), too, found differences as great as 10° to 12° between the 

 temperatures of air and water in Passamaquoddy Bay on individual days in July, 

 August, and September, whereas the maximum difference between air and surface 

 so far recorded for the open Bay of Fundy is only 7.34°; 8.3° for the Gulf of 

 Maine outside the outer headlands (on August 16, 1912). The mean difference 

 between air and surface temperatures for the Gulf of Maine as a whole will 

 probably be found to fall between 2° and 5° for the summer. 



We have occasionally found the surface shghtly warmer than the air as early 

 as the first week in August. In 1912, for example, the Grampus, running offshore 

 from Cape Elizabeth in a flat calm and bright sun on August 7 and 8, found the 

 water fractionally colder than the air early in the day, 1° to 1.5° warmer than the 

 air from noon to 2 p. m., once more slightly colder than the air from 3 to 9 p. m.. 

 and then again fractionally warmer than the latter from 10 p. m. until 1 a. m. 



A period is next to be expected when the air wUl be cooler than the water 

 duriug some of the nights, though still warming by day to a temperature higher 

 than that of the water, presaging the date (sometime in October) when the mean 

 temperature of the air falls permanently below that of the surface of the gulf, so 

 to continue throughout the winter. The following table of hourly differences will 

 illustrate this for one 24-hour period (August 15, 1 a. m., to August 16, 1 a. m.), 

 during which the Grampus ran eastward from the vicinity of Mount Desert Rock 

 toward the Grand Manan Channel. 



