EXPLANATION OF OCEAN TEMPERATURE CHART No. 19. 



POLLOCK Rir LIGHT-SHIP, MASSACHUSETTS. 



Ot.s(iros : William Haik.akd.s, J.vmks I'. Kklly, Joseph Allkx, .In. 



Localioii o/nlalioii. — This lightsbip i-s iDciited in tliu luii'thcastcni cutraucc to Nantucket or Viueyanl Sound, and 

 3J miles SE. bj^ E. i K. from Jlonomoy Point lislit-bouse, at the southeastern extremity of Capo Cod. It is IJ miles 

 distant from Pollock Riii Shoal proper, which lies between it and Monomoy Island, and is surrounded on nearly all 

 sides, at dilii-rent distances, by small shoals or groups of shoals. There is, however, no land to the northeast, east, or 

 southeast of it. It is anchored in a depth of 5 fathoms, and the deptbs about it range from 4 to 7 fathoms. The bot- 

 tom in this region consists of sand and gravel. Nantucket New South Shoal light-ship is about 3G miles nearly sonth. 



Geographical position.— LiitiUule, 41° 32' (27") N. ; longitude, €9° ^r,' (15") W. 



Depth of iiatci: — Five to 7 fathoms. 



Hange of temperature (March 1 to January 1).— Air, 3U° (21° to Gti°) ; surface, 30°.0 (3-2° to G2-.5). 



The curves of surface temperature are more irregular and less uniform than at the three or four preceding stations, 

 and in many cases the variations do not appear to be due to the influence of the air. They may be caused in part by 

 the currents flowing through the numerous passageways between the surrounding shoals. The ranges of teuiperat me 

 correspond closely with the same at Nantucket New South Shoal, the maximum air temperature being 3° lower at this 

 station, but the raaximuui and minimum for the surface are almost precisely alike at both. The nuiximum surTaee 

 temperature at Pollock Rij), located at the eastern entrance to Vineyard Souud, is .'JJ'^ lower than at Viney.ird Sound 

 light-ship, at the southwestern entrance to the same limly of water. 



Table showing the direction of the icinds, iy quadrants, fur each )nonlh of the ijear, being the nuans of fee gears' obscrrations. 



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