OCEAN TEMPEEATUKES. 171 



occasionally to much more. The differences are greater at some stations than at others, and are 

 seldom nearly the same at any station for two or more isotherms of different values. At Nan- 

 tucket New South Shoal, for example, the isotherms of 40° for five years, during the periods of 

 rising temperature, all appeared within four days of the same date, while those of 45° are 

 distributed over a period of about eighteen days. At the next station to the nortt — Pollock Rip— 

 the isotherms of 40° cover a period of over forty days, and those of 45°, a period of twenty -four 

 days. At Petit Manan the isotherms of 40° and 45° are rem,arkably constant in position from 

 year to year. The isotherms of 45° and 50° appear to be the most uniform in that respect for 

 their entire range during the five years; but no two isotherms of equal value retain the same 

 relative positions throughout their rang(\ There may be comparative regularity with respect to 

 several consecutive stations, but they generally cross one another one or more times, and while 

 the isotherm of 40° for 1881 precedes that of 40° for 1882, between Mount Desert and Pollock Rip, 

 at the more southern stations the reverse is true. The differences and irregularities in the posi- 

 tions of the yearly isotherms are so great that no definite laws respecting their relations over an 

 extended range of coast can be deduced from the materials used in the preparation of this report. 



GENERAL POSITIONS OP THE ISOTHEEMS. 



Forty degeees— The five isotherms of 40° (188l-'85), during the period of rising tem- 

 perature in the spring, pass from Winter Quarter Shoal to Fire Island in March and the first h alf 

 of April, from Block Island to Pollock Rip mostly iu April, and reach the Gulf of Maine in the 

 latter part of April or first half of May. At Petit Manan this temperature appears with great 

 regularity about the middle of April. During the period of falling temperature, the isotherms of 

 40° are confined for the most part to the. month of December, although they sometimes extend into 

 January of the following year, and, as a wiiole, are more nearly vertical in their direction than 

 those of the first half of the year. 



FoETY-FiVE DEGEEES.— From Winter Quarter Shoal to Fire Island the isotherms of 45°, 

 during the period of rising temperature, fall mostly within the month of April, but during two 

 years at Absecon Inlet, and one year at Winter Quarter Shoal, that temperature first appeared in 

 the last half of March. From Block Island northward the same isotherms extend, in a general 

 way, obliquely across the month of May into the first part of June at Matinicus Rock and Mount 

 Desert Rock ; they reach Petit Manan in the last of April or first part of May, or earlier than at 

 any other station in the Gnlf of Maine. During the period of falling temperature, the isotherms 

 of 45° in the Gulf of Maine are mostly confined to the month of November, and farther south to 

 the last part of November and December. 



Fifty degeees.— On the coast of South Carolina, the isotherms of 50° occur in January and 

 February, during the rise of temperature ; at Winter Quarter Shoal not until May, and at Absecon 

 Inlet in the last part of April and first half of May. From this point they extend obliquely across 

 the months of May and June, reaching Nantucket New South Shoal in the first part of June, 

 Matinicus Rock in July, Mount Desert Rock between May 24 and July 12, and Petit Manan 

 between June 8 and July 10. The same irregularities in the positions of the isotherms occur 

 during the period of falling temperature iu the Gulf of Maine, where they cover a period extend 

 ing from September 10 to November 26. From Pollock Rip to Absecon Inlet the same isotherms 

 are mostly limited to the month of .¥ovember, and from Five-Fathom Bank to Martin's Industry 

 they extend from the last of November into the first part of January. 



Fifty-five degeees.— None of the Tsotherms of 55° can be plotted continuously east of 

 Seguin Island, although at Petit Manan this temperature was recorded during all the four years 



