394 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
the surface had begun to grow warmer in Massachusetts Bay by this 
date (p. 391). At Boon Island, however, it was not until April 5 — 
that the first sign of spring warming was evidenced by the equaliza- 
tion of temperature (39°) from surface to bottom. From this time — 
onward, near the Isles of Shoals, there was a steady rise of tempera- 
ture, which made itself felt first and most strongly at the surface, and 
later, to a much smaller degree, at the bottom (fig. 4). But the 
surface warming was very irregular, and often interrupted, and even 
temporarily reversed, by climatic conditions. During the winter 
FATH 
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Ww. 
By 
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24 
Bi 
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FP EF Oe Oe GE at | 
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Fic. 4.— Temperature sections off Boon Island, March 29 (Station 5 W. W. 
Welsh); April 4 (Station 7 W. W. Welsh); and near the Isles of Shoals, 
April 13 (Station 11 W. W. Welsh); April 16 (Station 13 W. W. Welsh); 
April 26 (Station 19 W. W. Welsh); May 5 (Station 24 W. W. Welsh), 
May 13 (Station 29 W. W. Welsh) and May 14 (Station 30 W. W. Welsh). 
when the column of water is of nearly uniform temperature from the 
surface downward, offshore winds have little effect on surface tempera- 
ture, because although the surface water moves offshore, yet the 
waters which well up from below to take its place are of nearly the 
same temperature as those which they displace. But as soon as the 
surface 1s appreciably warmer than the underlying waters, any Up- 
welling, or vertical mixing, is at once evidenced by a decided drop in 
surface temperature. Along the coast, upwelling is usually the result 
of northwest winds; but any gale causes more or less vertical mixing 
of the upper few fathoms by wave action. How active these disturb- 
