THE TIDES. 



161 



them, when they are in the same straight line, 

 and to take a regular spheroidal form, in which 

 the difference between the greatest and the least 

 semi-diameter is about 2 feet for lunar action alone, 

 and i foot for the action of the sun alone that 



FIG. 20. Spring Tides. 



FIG. 21. Spring Tides. 



is a tide which amounts to 3 feet when the sun and 

 moon act together (Figs. 20 and 21), and to I foot 

 only when they act at cross purposes (Figs. 22 

 and 23), so as to produce opposite effects. These 

 diagrams, Figs. 20 to 23, illustrate spring and neap 

 tides : the dark shading around the globe, E, repre- 

 VOL. III. M 



