HISTORY OF THE AMKRICAN MtNHADEN. 53 



the monthly means of surface temperature; Table II, of temperature 

 at the bottom noar the shore; and Table III, the a\"eiaj:;;e a)eans of the 

 surface and botcoin temperatures. Tlie ol)st'rvations were all made at 

 3 p. ra., and are continuous from March 1, 1870, to March 1, 1877. These 

 are reproduced in Appendix K. There is, also, a table of the daily (»b- 

 servations of temperature at the surface at the same stations. A study 

 of these tables, which, for convenience, were mappe<l out in curves upon 

 section paper, affords some intenisting results. 



MiniiHiOH limits of temperature and the dates of appearance and disap- 

 pearance of the schools. — The monthly mean of surface temperatures at 

 Eastport is greatest in September, when it is SO^.G, while the highest 

 daily observation is 51<^.o. The menhaden do not visit Eastport in mid- 

 summer. Let us divide the monthly averages for May, at Portland, into 

 quarterly periods. The average for May 16-23 is 47°. 1 ; for May 24-31 

 is 51°. The quarter-mouth averages for October are 53o.8, oOo. 8, 470.9, 

 480.8. 



The schools of menhaden arrive in Eastern Maine late in May and 

 early in June, and depart, usually, before the middle of October. 



At Wood's HoU the quarter-month averages for May, as taken by the 

 Signal Service observer, are 48o.2, 49o.0, 53o.l, and 570.0, approximately, 

 or the monthly average, 520.3. These observations are made in the 

 Great Harbor, at the railroad-wharf. Auother series of observations, 

 made by Captain p]dwards, for the Light-House Board, in the Little Har- 

 bor, are believed to indicate more nearly the temperature of the Vineyard 

 Sound. These, however, are only for bottom. The <liflfereuce between 

 the monthly mean of bottom temperatures for May, at the two stations, 

 is almost two degrees (1°.8), the figures being 51^.5 for Great Harbor, 

 for Little Harbor 53^.3. It does not seem assuming too much to place the 

 quarter-month average for the first half of May at 50"^ and 51o.4. For 

 November the Great Harbor quarter-month means are 51°, 51°, 47o.7, 

 430.3. 



The menhaden strike into Vineyard Sound early in May or late in 

 April, and linger until November, and even December. 



At New London the quarter monthly averages for the last half of 

 April and the first half of May are 49°, 48o.5, 52o.o, 54o.5 ; lor late Oc- 

 tober, 550.2, 540.9 ; for November, 53o.5, 51o.l, 480.I, 46o,l. 



The fish come on the eastern coast of Connecticut late in April, and 

 are frequently taken as late as the middle of November. The temperatures 

 of New London suggest that there may be something in error in the Wood's 

 HoU observations in so far as they are supposed to indicate the temper- 

 ature of the ocean in its immediate vicinity. The periods of appearance 

 and disappearance at Waquoit and Menemsha, in the Vineyard Sound, 

 agree nearly with tliose of Eastern Connecticut. 



The temperature of the Chesapeake must be studied from the obser- 

 vations made at Baltimore and Norfolk. At the latter place the April 

 means are 52o, 56o.5, 61 0.2, GQo ; the November means, 59o, 540.6, 53o.5, 



