BIGELOW: OCEANOGRAPHY OF MASSACHUSETTS BAY. 395 



ing factors were off the Isles of Shoals during the spring of 1913 is 

 illustrated by the diagram of surface temperature (fig. 7). After a 

 steady rise from 38.3° to 41°, a northwesterly gale cooled the surface 

 to 40.3° by upwelling. It then warmed once more, under the influence 

 of unseasonably warm weather, to 46.3° on April 26, when a north- 

 easterly gale and rain, followed by high northwest wind, once more 

 lowered the surface temperature to 44°. This was followed by 

 another rise to 49° when a third northwesterly gale blew for several 

 days, with the result that the surface was cooled to about 45°. When 

 the wind changed to the south, the surface once more grew warmer, 

 its temperature being 46.6° on May 14, when the latest observation 

 was made. These surface irregularities are traceable down to about 

 5 fathoms (fig. 4) below which depth the progressive warming was 

 comparatively regular. Until April 19 warming was limited to the 

 upper 15 fathoms, below which depth the temperature was about 

 39.3° to the bottom (the deepest observations were at 30 fathoms) ; 

 but by May 5 this temperature was found only below 20 fathoms, and 

 from that time onward there was a slight rise in the bottom tempera- 

 ture to 39.9° on the 14th (latest station). This is about 2° colder than 

 it was at this depth (30 fathoms) in this same region in the summer 

 of 1912, but only about 1° lower than the water in the deeper parts of 

 the basin between Jeffrey's Ledge and the mainland at that time. 



The Boon Island stations (fig. 5) show that salinity reaches its 

 maximum here in early spring just as it does southeast of Cape Ann. 

 Unfortunately the observations do not show exactly what the maxi- 

 mum was for there is a gap in the data at the critical time from April 

 5 to April 13: but the fact that the salinity was 32.45%^ on the sur- 

 face, 32.99%o at 40 fathoms, March 29, with a mean of about 32.76%o 

 for the entire column of water, rising to 32.74%c on the surface, 

 33.04%o at 32 fathoms, on April 5, suggests that the maximum was 

 about the same here as it is on the other side of Cape Ann. But 

 whether or not this is the case, it is certain that in 1913 the maximum 

 salinity was not reached off Boon Island until at least a week after 

 surface freshening had begun to show itself in Massachusetts Bay. 

 The numerous observations near the Isles of Shoals show a marked 

 decline in salinity in that region from the middle of April till the middle 

 of May, i. e., from 31.43%o to 29.54%o followed by an irregular rise 

 which was still in progress when the work came to an end. And a 

 glance at the salinity curve for the surface (fig. 7) shows that it agrees 

 closely with the temperature curve, periods of temporarj^ cooling cor- 

 responding to a temporarily heightened salinity, surface salinity being 



