BIGELOW: OCEANOGRAPHY OF MASSACHUSETTS BAY. 391 
fathoms the temperature was 41.7°, practically the same as it was at 
the same depth on the Massachusetts Bay side of Cape Ann. The 
surface salinity, likewise, was much lower on the surface in Ipswich 
Bay, 32.20% ; but at 19 fathoms it was slightly higher, 32.9% as 
against 32.82% . Of course it is impossible to be certain of the rea- 
sons for these differences, without any data on conditions in Ipswich 
Bay during the preceding three months, but the simplest, and proba- 
bly the correct explanation for its low surface temperature is that the 
snow-fall in the recent storm was heavier there than over Massachu- 
setts Bay, for melting snow ranks second only to melting ice as a 
cooling agent for surface waters; while the low surface salinity is no 
doubt an indication of the fresh water from the Ipswich and Merrimac 
rivers which empty near by. 
The minimum temperatures for the winter were reached about the 
middle of February. Thus on February 13, at a station some five 
miles southeast of Cape Ann, the surface temperature was only 37.1°, 
with 37° at 25 fathoms, and 37.6° on the bottom in 45 fathoms: 
thus reflecting the wintry weather which had at last set in after an 
unusually mild season. At this station the air temperature was 20°, 
with a high northwest wind, and during the preceding night the 
thermometer had fallen to —2°. Salinity differed little from what was 
found at the last station but one in Massachusetts Bay, being 32.83% 
on the surface and at 25 fathoms, 32.84%, on the bottom. And the 
fact that the difference between surface and bottom salinity was so 
slight is as good evidence as are the inverted temperatures, of active 
vertical circulation, for there had been two falls of snow since the last 
visit. And as a matter of fact, the water was in unstable equilibrium, 
the density being 26.19 at the surface, 26.18 on the bottom (pressure 
disregarded). 
By March 4, when we made the next station some five miles east of 
the usual location, choosing this point because of the slightly greater 
depth (45 fathoms), both the weather and the water showed signs of 
| spring warming, the surface temperature having risen by .1°, to 37.2°: 
at 25 fathoms by .5° to 37.5°, and at 45 fathoms by .9° to 38.5°, the air 
temperature being 32° with light snow falling. At the same time the 
,, Water samples showed a decided rise in salinity, the surface being 
| 82.85%o, with 32.96% at 25 fathoms, and 33.04%, at the bottom, 
| the latter a much higher salinity than any which we had previously 
| obtained in Massachusetts Bay. In summer, water as salt as this was 
| first found on the bottom some 35 miles east of the mouth of the Bay. 
| The water was now once more in stable equilibrium (density at sur- 
