CAUSES OF TIDES. 47 



influence of the moon, which, to a small extent, 

 lifts the waters of the ocean towards it as it passes 

 over them, and thus causes a high wave. This 

 wave, or current, when it swells up on the land, 

 forms high tide. When the moon's influence has 

 completely passed away, it is low tide. The moon 

 raises this wave wherever it passes; not only in 

 the ocean directly under it, but, strange to say, it 

 causes a similar wave on the opposite side of the 

 globe. Thus there are two waves always follow- 

 ing the moon, and hence the two high tides in the 

 twenty-four hours. This second wave has been ac^ 

 counted for in the following way : The cohesion of 

 particles of water is easily overcome. The moon, in 

 passing over the sea, separates the particles by her 

 attractive power, and draws the surface of the sea 

 away from the solid globe. But the moon also at- 

 tracts the earth itself, and draws it away from the 

 water on its opposite side, thus causing the high 

 wave there, as represented in the diagram, fig. 1. 



-e 



Fig. 1. 



The sun has also a slight influence on the tides, but 

 not to such an extent as the moon. When the 

 two luminaries exert their combined influence in 

 the same direction, they produce the phenomenon 



