PHYSIOLOGICAL PARADOXES. 



more than two thousand years ago, we can 

 hardly help believing there is a real and natural 

 limit to the divisibility of matter that is to 

 say, substances are constructed of small par- 

 ticles or granules which are themselves in- 

 destructible and indivisible. 



The conception of matter as not infinitely 

 divisible makes it easier to think of motion in 

 the same way. But for those who find a diffi- 

 culty in believing that a thing may be true 

 without having an idea of some way in which 

 or some means by which it can be true, it will 

 be helpful to consider, by way of illustration, 

 the details of arrangements which would bring 

 about the same state of things on a larger scale. 



Suppose that ten acres of ground were 

 divided into squares of one yard each in the 

 manner shown in Fig. 61. Let each square 

 yard be covered by a board of the same size, 

 which is swung on pivots so that by suitable 

 electric connections and power contrivances it 

 can be quickly turned over. Let all the boards 

 be green on one side and red on the other. 



If this piece of ground be viewed from a 

 great height on a distant mountain, when all 

 the boards have their green sides uppermost, 

 it will look much like an ordinary green field 

 of very uniform colour say a field of young 

 wheat. The distance will be too great for any 

 of the boards or the divisions between them to 

 be visible. 



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