588 BULLETIN OF THE BUREAU OP PISHEBIES 



northern shores of Massachusetts Bay usually remains cooler than 18° on the sur- 

 face throughout the summer, though warmer than 15°; hut as every bather knows, 

 continued onshore winds sometimes drive the warm offshore water right in to the 

 beach there, though in a surface film so thin that one's legs may be in decidedly 

 lower temperatures while swimming. On the other hand, when westerly winds 

 drive the surface water out to sea, cooler water wells up from below, locally lowering 

 the surface temperature. Upwellings ofthis sort, combined with local stirrings by 

 the tides, are so common an event along the northern shore of the bay that usually 

 this is fringed by a zone, a few miles wide, where streaks of surface water warmer 

 than 16° alternate irregularly with patches cooler than 14° to 15°, and where we 

 have occasionally had surface readings as low as 12° in July, with 10° reported to 

 us in August. Cold streaks of this sort are most often to be expected about the 

 bold promontory of Nahant and along the rocky shore between Gloucester and 

 Cape Ann. 



At Thatchers Island (the tip of Cape Ann) tidal disturbances may cause consid- 

 erable and irregular fluctuations in the temperature of the surface from day to day, 

 witness readings varying from 15.6° to 17.5° during the warmest periods of the 

 summer of 1881 (Rathbun, 1887); but a temperature of 19.4° at the cape late in 

 July, 1882, shows that the warm surface water from offshore may touch the coast 

 line there during calm periods or after onshore winds, as it does elsewhere. 



It appears from what little precise evidence is available, and from general 

 reports by seaside dwellers, that similar fluctuations prevail aU along the coast line 

 in August, from Cape Ann northward about to Cape Porpoise; but the surface of 

 the coastal belt averages 1° to 2° colder in this sector than in Massachusetts Bay — 

 usually below i6°. 



It is unfortunate that daily records are not available for any station along this 

 stretch of coast Hne or for the Isles of Shoals, which occupy a commanding position 

 off the mouth of the Merrimac River. Most of our August passages, also, to and 

 fro, have followed courses outside the 100-meter contour. Rathbun's (1887) record 

 of maxima of 15.6° to 16.7° at Boon Island for the summers of 1881 to 1885, with 

 our own stations between Cape Elizabeth and Cape Ann, suggest 15° to 16° as the 

 usual maximum for the coastal sector between the Isles of Shoals and Cape Eliza- 

 beth, out to the 100-meter contour, with temperatures 1° to 3° higher a few miles 

 farther out at sea. 



The rise in surface temperature experienced as one runs offshore from Cape 

 Elizabeth is illustrated by the following readings taken by W. C. Schroeder on the 

 Halcyon on a trip to Platts Bank, July 20, 1915: 8 miles out from Cape EHza- 

 beth, 16.1°; 173^ miles out, 19.44°; 20 miles out, 19.44°; on Platts Bank, 30 miles 

 out, 18.9°. This agrees closely with the gradation indicated for this region on 

 the charts (figs. 46 and 47); also with the state of the surface on August 7, 1912, 

 when the temperature rose, progressively, from 15.6°, at a point 8 miles off the 

 cape, to 17.8° on Platts Bank (Bigelow, 1914, p. 46). 



It has long been common knowledge that the coastal waters along eastern Maine 

 and in the Bay of Fundy are cold in summer, with a maximum difference of almost 10° 

 C. (18° F.) between the surface there and in the offing of Cape Ann. This cold area, 



