Tlie Tides. 213 



on account of their density, contain a greater mass, and gravity 

 acting upon this mass gives theru their preponderance, at the same 

 time one volume will respond to the force of gravity as readily 

 as another, nothwithstanding their different densities. 



A tide occurs at opposste sides of the earth at the same time, 

 that is, one tide follows the upper transit of the moon and another 

 the lower one in the same place. The water is said to be drawn 

 away from the earth on one side and the earth away from the 

 water on the remote side. 



"We know that two forces acting in the same direction are rep- 

 resented by a simple sum of these forces and that attraction act- 

 ing from one side through a body upon matter on the opposite 

 side will only aid gravity in holding that matter more securely on 

 that side, but, it is admitted that matter is heavier on the earth's 

 surface on the side remote from the sun, which fact recalls the 

 argument, that if anything is affected by foreign attraction it will 

 be affected most by the superior force, 



Argumeet a-ide, the tide is certainly obedient to the moon, but 

 the manner in which this is brought about, is the problem to be 

 solved. 



One feature of the phenomena which is used to show that the 

 tide is raised by attraction, is the difference in range of the semi- 

 diurnal tides at different positions of the moon, the higher tide 

 succeeding the superior transit and north declination and the lower 

 transit during south declination, showing that the moon draws 

 the water after it. 



Now let us see how true this is. 



The Atlantic tide is created in the southern part of the South 

 Atlantic ocean, and moving eastward reaches the African coast 

 shortly after the moon's transit at that place. Thence it moves 

 north and west, reaching the United States coast twelve hours 

 later. The other side of the wave in connection with the Arctic 

 tide moving east and north, reaches Ireland four hours later, and 

 Dover straits twelve hours later still ; so that in some places it is 

 the tide after moon's transit, and in others the previous tide 

 which is observed, so that the facts become reversed. 



Nearly all authors on this subject — the tides — ^are satisfied 



