ELEMENTARY THEORY OF THE TIDES. 



THE attractive force of the sun or moon on the solid mass 

 of the earth is the same as if the latter were concentrated 

 at the centre. But the attractive force, on movable par- 

 ticles at the surface, is greater than this on the side nearest 

 to the moon (or sun), and less on the opposite side. Thi& 

 excess and defect constitute the tide-producing force. 

 Confining ourselves to the moon : 



The direction of the tide-producing force is always tangen- 

 tial, and towards the line joining the centres of the Earth 

 and moon. 



The following (Newton's) construction represents this 

 force in direction and magnitude. 



Fig. i. 

 I 



Let xl (fig. ~^) be perpendicular to EH, and let Im = mn 

 = EL Then if ME represent the attractive force of 

 the moon at the centre E, xn will represent the whole 



B 



