WHAT DID THE ANCIENTS KNOW OF TIDES ? 37 
attracts the ocean, and thus tides arise in the larger seas. If 
the earth ceased to attract the waters, they would rise and flow 
up to the mocn.” 
The general notion of a mutual attraction, however, did no 
more than point out the way for the solution of the problem, 
and it was reserved to our great Newton 1o accomplish the 
prophecy of his great predecessor, *‘ that the discovery of the true 
laws of gravitation would be accomplished in a future generation, 
when it should please the Almighty Creator of nature to reveal 
her mysteries to man.” 
Newton was the first who proved that the tide-generating 
power of a celestial body arises from the difference of the at- 
traction it exerts on the centre and the surface of the earth. 
Thus it was at once made clear how the water not only rises on 
the surface facing the moon, but also on the opposite side of the 
earth, as in the latter case the moon acts more strongly on the 
mass of the earth than on the waters which cover the hemisphere 
most distant from her. The evident consequence is that the 
earth siiks (so to say), on the surface turned from the moon, 
whereby a deepening of the waters, or, in other words, a rising of 
the tide, is occasioned. 
It now also became clear how the moon, whose attractive 
power upon the earth is 160 times smaller than that of the 
sun, is yet able to occasion a stronger tide, since, from her 
proximity to the earth, she attracts the surface more forcibly 
than the centre with the thirtieth part of her power, while the 
distant sun occasions a difference of attraction on these two 
points equal only to one twelve-thousandth part of her attrac- 
tive force. 
Now also a full explanation was first given why the highest 
tides take place at new and full moon: that is, when the moon 
stands between the sun and the earth; or the latter between the 
sun and the moon; as then the two celestial bodies unite their 
powers; while at half-moon the solar tide corresponding with 
the lunar ebb, or the lunar tide with the solar ebb, counteract 
each other. 
But even Newton explained the true theory of the tides only 
in its more prominent and general features, and the labours of 
other mathematicians, such as MacLaurin, Bernoulli, Euler, 
La Place, and Whewell, were required for its further development, 
