EXPLANATION OF OCEAN TEMPERATURE CHART No. 26. 



Isothermal lines connecting the series of light-house stations on the eastern coast of the United States, represented 

 on Chart No. 1, constructed for every 5° of temperature, Fahrenheit, from 40° to 80°, inclusive, for the year 1881. 



A temperature of 55° was reached at Mount Desert Eock between June 24 and 30, but otherwise the isotherms of 

 55° extend north only to Segnin Island. At Nantucket New South Shoal, 60° was recorded continuously for eight 

 days only, or from August 7 to 14. Two very short periods of higher temperature than 75° occurred at Absecon Inlet 

 ^ July 14 to 20, September 30 to Octpber 24), but the isotherms of 75° begin regularly at Winter Quarter Shoal, where the 

 interval between the two lines is only eight days (July 13-20). During the period of falling temperature, the isotherm 

 of 40° extends south continuously within the year to Fire Island, although at Pollock Eip, Nantucket New South 

 Shoal, and Vineyard Sound observations are lacking for that temperature. At Sandy Hook the isotherm of 40° was 

 not reached until February, 1882, while at Five Fathom Bank and Winter Quarter Shoal the temperature remained 

 above 40° during the entire winter of 1881 and 1882. The isotherm of 50° extends south only to Cape Lookout in the 

 same winter, but in the early part of 1881 it reached to Martin's Industry. At the Tortugas the temperature fell below 

 70° during a short period just prior to February 8, and again between March 20 and April 15. 



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