PHYSICAL OCEANOGEAPHY OP THE GULP OF MAINE 



587 



whence the hmiting isotherm (18°) spreads south as well as north, to the confines 

 laid down on the chart, as the summer draws to its close. 



We have invariably had surface readings higher than 18° in the outer half of 

 Massachusetts Bay after the first week of August, and in Cape Cod Bay; but off 



TV 



Fig. 46. — Normal surface temperature for mid-August, based on a combination of the recent station records with Hathbun's 

 (1887) tabulation at lighthouses, the Canadian records, Dickson's (1901) data, and the daily surface readings, at 

 Gloucester, Boothbay, and Lubec (flgs. 29 to 31). (Close to Cape Sable, read < 10° for > 10°.) 



the tip of Cape Cod, where tidal currents run strong, the surface is usually cooler 

 locally, as is the general rule in such locations, with readings of 17° to 18° for the 

 last half of August. For this same reason the coastal belt around the western and 



