290 The Outline of Science 



discovered. It is Einstein who, by revolutionising our conceptions 

 of space and time, showed that no such motion ever could be 

 discovered, whatever means were employed, and that the usual 

 notion of the ether must be abandoned. We shall explain this 

 theory more fully in a later section. 



INFLUENCE OF THE TIDES: ORIGIN OF THE 

 MOON: THE EARTH SLOWING DOWN 



16 



Until comparatively recent times, until, in fact, the full 

 dawn of modern science, the tides ranked amongst the greatest 

 of nature's mysteries. And, indeed, what agency could be in- 

 voked to explain this mysteriously regular flux and reflux of the 

 waters of the ocean? It is not surprising that that steady, rhyth- 

 mical rise and fall suggested to some imaginative minds the 

 breathing of a mighty animal. And even when man first became 

 aware of the fact that this regular movement was somehow 

 associated with the moon, was he much nearer an explanation? 

 What bond could exist between the movements of that distant 

 world and the diurnal variation of the waters of the earth? It 

 is reported that an ancient astronomer, despairing of ever resolv- 

 ing the mystery, drowned himself in the sea. 



The Earth Pulled by the Moon 



But it was part of the merit of Newton's mighty theory of 

 gravitation that it furnished an explanation even of this age-old 

 mystery. We can see, in broad outlines at any rate, that the 

 theory of universal attraction can be applied to this case. For 

 the moon, Newton taught us, pulls every particle of matter 

 throughout the earth. If we imagine that part of the earth's 

 surface which comprises the Pacific Ocean, for instance, to be 

 turned towards the moon, we see that the moon's pull, acting on 

 the loose and mobile water, would tend to heap it up into a sort 



