EXPLANATION OF OCEAN TEMPERATURE CHART No. 31. 



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, being the means of 

 five years' observations, from 1881 to 1885, inclusive. 



Most of the plottings on this chart are reductions of the observations of five years, bnt in some cases they rep. 

 resent a shorter period, though seldom less than four years, and never less than three years. The exact number of 

 observations in each case.may be determined by reference to the five preceding charts (Nos. 26-30) on which the iso- 

 therms for each year are separately shown. At Thatcher's Island, Massachnsetts, no records were kept after the sum- 

 mer of 1883, and at Body's Island, Virginia, observations ceased to be taken after October of the same year. At none 

 of the other stations, however, do serious breaks in the records occur, and there are seldom more than one or two 

 omissions at any station. 



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