BIGELOW: OCEANOGRAPHY OF MASSACHUSETTS BAY. 393 



(fig. 2) the surface salinity had fallen from 32.8%o to 32.3%o (fig. 3), 

 which is, of course, good evidence that the influx of river water was 

 beginning to flood the surface. And from the standpoint of dynamics 

 this phenomenon is important, because it suddenly lowers the surface 

 density to a marked degree, wnith consequent increase in vertical 

 stability. Unfortunately only two more stations were occupied in 

 Massachusetts Bay during the spring; but though both were so close 

 to land that thej^ are not strictly comparable with the data acquired 

 further offshore, they show the advance of the general vernal hydro- 

 graphic change. Thus on April 14, two miles off the mouth of Glou- 

 cester Harbor, the surface temperature had risen to 42°, the 25 

 fathom reading (bottom) being about the same as at the last station 

 (39.4°). And on May 17, the surface water off ISIagnolia had warmed 

 up to 47.3°, with 45.1° at 9 fathoms. Salinity meantime had fallen 

 to 31.11%(; on the surface, 32.79%o ^^ 25 fathoms, on April 14: and it 

 continued to fall, reaching 30.95%o on the surface, 31.25%c at 10 

 fathoms on Mav 17. 



Temperature .^^;D salinity north of Cape Ann, 

 ISIarch .and April. 



]Mr. Welsh's oceanographic data for these months were taken chiefly 

 in three general regions, i. c, the neighborhood of the Isles of Shoals, 

 near Boon Island, and a few miles off the coast between Cape Porpoise 

 and Wood Island (Plate) ; and though his stations were chosen pri- 

 marily for their fisheries interest, they proved to be well located for 

 oceanographic purposes. The first two grounds together cover an 

 area of some fifteen miles from northeast to southwest; but there 

 is no important separation between the two, so far as temperatures 

 are concerned. The salinity of the area, however, is less uniform, be- 

 cause subject to the immediate influence of the Piscataqua River. 

 The Cape Porpoise ground, though nearer in actual distance to the 

 Boon Island stations than the latter are to the Isles of Shoals, was very 

 distinct hydrographically. 



The Boon Island ground was visited on March 29, April 4, April 5, 

 and May 14, while from April 22 to May 16 frequent observations 

 were taken close to the Isles of Shoals and between them and the 

 coast. On the first date the water was coldest at the surface, the 

 readings being 38.3° at the surface, 38.7° at 17 fathoms, and 38.9° 

 at 35 fathoms; i. c, winter conditions still prevailed (fig. 4), although 



