108 



'U. S. COAST AND GEODETIC SURVEY 



As related to the moon's changing phases, the variation in the strength of 

 the current from day to day is approximately proportional to the corresponding 

 change in the range of the tide. The moon's changing distance likewise brings 

 about changes in the velocity of the strength of the current which is approxi- 

 mately proportional to the corresponding change in the range of the tide; but in 

 regard to the moon's changing declination, tide and current do not respond alike, 

 the diurnal variation in the tide at any place being generally greater than the^diur- 

 nal variation in the current. ' ^ 



Scale o-F Knots 

 J I I I 



0.0 0.2 0.4 0.6 0.8 1.0 \Z 1.4 



Fig. D.— Rotary current, Nantucket Shoals laght Vessel, afternoon of September 24, 1919 



The relations subsisting between the changes in the velocity of the current 

 at any given place and the range of the tide at that place rnay be derived from 

 general considerations of a theoretical nature. Variations in the current that 

 involve semidiurnal components wiU approximate corresponding changes in the 

 range of the tide; but for variations involving diurnal components the variation 

 in the current is about half that in the tide. 



