58 THE YEAR. 



duced by the one can never be farther from one pro- 

 duced by the other than a quarter or quadrant of the 

 earth's circumference ; because, when the upper tides, 

 or those that are produced at the points where the lu- 

 minaries are vertical, separate to a greater distance 

 than that, the under tide of each will approach just as 

 much nearer to the upper tide of the other. They will 

 therefore be at the same meridian, or directly north and 

 south of each other, at new moon when the moon is in 

 conjunction with the sun, and at full moon when it is 

 in opposition ; and they will be at the greatest distance, 

 at the end of the first and third quarters of the moon. 

 When they are at the same place they will act jointly, 

 and when at separate places they will act against each 

 other, the more, the further flhat they are separate. The 

 action of the moon in producing this disturbance is, 

 however, so much greater than that of the sun, because 

 the moon is so very much nearer to the earth that half 

 the diameter produces a much greater variation in its 

 action, that the general tide follows the moon, and the 

 sun only modifies it by augmenting it to a spring tide 

 at full and change, and depressing it to a neap tide 

 at the quarters. 



Those actions of the sun and moon occasion two 

 motions of the ocean and the atmosphere in the general 

 directions of from east to west, the one following the 

 sun and apparently passing round the earth in twenty- 

 four hours, and the other following the slower course 

 of the moon, and taking about fifty minutes more to 

 encompass the earth. It must not be supposed, how- 

 ever, that those motions are attended by an actual 

 transfer of the water of the ocean or the atmospheric 



