ERRONEOUS NOTIONS CORRECTED. 



force, would equally tend towards the moon ; and its parts v whether 

 solid or fluid, would preserve among themselves the same relative 

 position as if they were not attracted at all. 



4. When we observe, however, in a mass composed of various 

 particles of matter, that the relative arrangement of these par- 

 ticles is disturbed, some being driven in certain directions more 

 than others, the inference is, that the component parts of such 

 a mass must be placed under the operation of different forces ; 

 those which tend more than others in a certain direction being 

 driven with a proportionally greater force. Such is, in fact, the 

 case with the earth, placed under the attraction of the moon. 

 Newton showed that the law of gravitation is such, that its 

 attraction increases as the distance of the attracted object dimi- 

 nishes, and diminishes as the distance of the attracted object 

 increases. The exact proportion of this change of energy of the 

 attractive force, is technically expressed by stating that it is in the 

 inverse proportion of the square of the distance ; the meaning of 

 which is, that the attraction which any body like the moon would 

 exercise at any proposed distance, is four times that which it 

 would exercise at twice the distance ; nine times that which it 

 would exert at three times the distance ; one-fourth of that which 

 it would exercise at half the distance, and one-ninth of that which 

 it would exercise at one-third the distance, and so on. Thus we 

 have an arithmetical rule, by which we can with certainty and 

 precision say how the attraction of the moon will vary with any 

 change of its distance from the attracted object. Let us see how 

 this will be brought to bear upon the explanation of the effect of 

 the moon's attraction upon the earth. 



Let A, B, c, i>, E, F, G, H, represent the globe of the earth, 

 and, to simplify the explanation, let us first suppose the entire 

 surface of the globe to be covered with water. 

 Let M be the moon, and let H be the nearest, 

 and D the most remote part of the earth. 

 Now it will be very apparent that the various 

 points of the earth's surface are at different 

 distances from the moon: A and G are more 

 remote than n ; B and F still more remote ; c 

 and E more distant again, and D most remote 

 of all. The attraction which the moon exercises 

 at H is, therefore, greater than that which it 

 exercises at A and G, and still greater than that 

 which it produces at B and F ; and the attrac- 

 tion which it exercises at D is least of all. Now 

 this attraction equally affects matter in every state and con- 

 dition. It affects the particles of fluid as well as solid matter, 



K 2 131 



