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THE TIDES 19 



on the moon at this time he would see the ring of Hght around the 

 black earth-globe brilliantly crimsoned; at other parts it would 

 have shades of red and yellow, and the whole effect would be to 

 make the "grand earth-ball, hanging in the lunar sky, like a dark 

 sphere in a circle of glittering gold and rubies." 



The reason there is no eclipse at every full moon is because the 

 moon's orbit is at an angle of about five degrees to the ecliptic 

 in which the earth moves and in which its shadow always lies, so 

 it is only occasionally that the two are in a straight line from the 

 sun. To appreciate an eclipse of the moon we should try to think 

 how far away from us the moon is. Ball says "An express train 

 which runs 40 miles an hour would travel 240 miles in six hours, 

 and the whole distance to the moon would be accomplished in 

 6,000 hours, so that by travelling night and day incessantly you 

 would accomplish the journey in 250 days." 



It seems very wonderful that our earth can cast a shadow as far 

 as that. 



The Tides 



When Newton discovered the laws of gravity he made a very 

 great discovery about something of which even at this late day 

 we know very little. Why bodies of matter attract each other 

 has seemed a wonderful fact that we could not explain. How- 

 ever the physicists think they are on the hot trail of the truth now 

 and may be we shall soon receive enlightenment concerning this 

 miraculous force that welds the stars together as surely as it causes 

 the little child to fall if he loses his balance. 



We have long known that the tides that sweep over great bodies 

 of water are caused by the pulling of the moon. This is really 

 lifting the water and incidentally pulling it as the moon moves 

 around the earth. If the oceans covered the entire earth the high 

 tide would be regular, but owing to the irregularities of the land, 

 and the varying depth of the water, the tide is much affected as to 

 height and direction. It is easy enough to understand how the 

 moon can cause one tide each day, but it is not so evident how it 

 causes two. At the same time that the moon is lifting the waier in 

 the oceans toward it and away from the earth, it is lifting the earth 

 away from the ocean on the opposite side of the earth and this 

 results in a rising of the water there which results in another high 

 tide just half of a day later; thus we have two tides each day, the 



