76 INTRODUCTION TO GENERAL SCIENCE 



e. 1003 : 112-132. The Moon, Tides, and Eclipses. 



/. 1004: 117-125. Physical Characteristics of the Moon. 



g. 1306 : 13-15. The Moon, Tides, and Eclipses. 



55. TIDES 



The chief effect of the moon upon the earth is the produc- 

 tion of tides in the ocean. The earth and the moon are at- 

 tracted each by the other, but since the water is more mobile 

 than the solid earth, the ocean piles up on the side nearest the 

 moon and forms what is called high tides. These tides, out 

 in the ocean, are about four feet above mean sea level. Near 

 the shore tides may be much higher on account of the shape 

 of the bays. Not only is there a high tide nearest the moon, 

 but there is another on the side of the earth opposite to the 

 moon, and in between these two tides are two low tides, on 

 opposite sides of the earth. In a general way, the explana- 

 tion is as follows: Since the water on the side of the earth 

 farther away from the moon is not attracted as strongly as the 

 earth is, the latter is pulled away from the water, leaving the 

 water apparently high. The scientific explanation of tides 

 belongs properly to advanced physics. 



The sun also produces tides on the earth which are very 

 slight compared with the moon's tides. However, if both the 

 sun and the moon are on the same side, or opposite sides, of 

 the earth, the result is that both act together to produce an 

 extra high tide. These tides, which occur about twice a month, 

 are called spring tides. If a line from the moon to the earth 

 forms approximately a right angle with a line from the earth 

 to the sun, the effect of th sun on the water is to reduce the 

 moon tides slightly; these tides, which also occur about twice 

 a month, are called neap tides. 



