342 



PHYSIOGRAPHY 



(new moon), each tends to make high tides at A and at B. When 

 the relations are those shown in Fig. 269 (full moon), the result is 

 the same. At these times, and each occurs once a month, the 



^_^ 



Fig. 268. Diagram to show the relative positions of the earth, moon, and 

 sun, at the time of new moon ( = spring tide). 



high tides are higher and the low tides lower than at other times. 

 The tides of such times are called spring tides. Spring tides have 

 no relation to the spring season. 



Fig. 269. Diagram to show the relative positions of the earth, moon, and 

 sun, at the time of full moon ( = spring tide). 



When the earth, moon, and sun have the relative positions 

 shown in Fig. 270, and this occurs twice each month, the tidal 

 influences of the sun and the moon are opposed to each other, and 



Fig. 270. Diagram showing the tendency of the sun and moon to produce 



A 1 A A f i i i ^ j i i r , i i ,!, 



tides on opposite parts of the earth at the time of the quadrature, tlmt is 

 at a time half-way between new moon and full moon, or half-way between 

 full moon and new moon. 



the result is that the high tides are not so high, or the low tides so 

 low, as under other conditions. The tides of such times are known 

 as neap tides. 



