450 



BULLETIN OF THE BUREAU OF FISHERIES 



2. The magnitude of this movement varies with the range of tide, and both are 

 greatest when the moon is full and in perigee. 



3. Since the temperatures of the air and land are highest in July and August, 

 their effect on water temperature will be greatest during the periods of maximum 

 range of tide. 



4. Taking into consideration meteorological conditions, the daily and hourly 



temperature fluctuations can be correlated closely with changes in the stage and 



range of tide. 



TIDE AND CURRENT 



In discussing tidal phenomena, the term "tide" is used to designate the vertical 

 movement of the water and "tidal current" to designate the horizontal movement.' 

 In the various bays and estuaries along the coast the tidal movement is determined 



rc 



20 



»8 



12 

 (0 



24 



6 ;2 /8 24 6 (2 18 24 6 \Z f8 



JUNE i\)U AUGUST 



FiGiiRE 12.— Comparison of the water temperature at the mouth of Long Island Sound in 1926 and 1926 



largely by the type of ocean tide that enters them and is modified by the configiu-ation 

 and hydrographic features of the coast in each locality. On the Atlantic coast of 

 the United States the ocean tide is of the semidiurnal type, the chief characteristics 

 of which are that (1) two high and two low waters occur during each tidal day, and 

 there is but little difference between morning and afternoon tides; (2) the rise and 

 fall of the tide varies from day to day according to the position and phase of the 

 moon; (3) spring tides follow full and new moon by one day and are 20 per cent 

 greater than the average, while neap tides follow first or third quarters of the moon 

 by one day and are 20 per cent less than the average; and (4) the duration of rise 

 and the duration of fall of tide are equal, each being about 6 hours and 12 minutes. 

 These are also the general characteristics of the tides in Long Island Sound and MU- 

 ford Harbor. As the ocean tide enters a partially inclosed basin along the coast, 

 it produces considerable variation in the physical conditions e.xisting there, such as 

 salinity, temperature, H-ion concentration, etc. The hydrography of the region and 

 the range of tide determine largely the extent of variation that is produced. From 



• In this discussion of tide, statements frequently are taken from "The Tide," by H. A. Marmer, 1926. 



