THE TIDES 293 



the sun or of the moon, or of both, thtn we must call it a 

 tide. 



It is curious to look back on the knowledge of the tides 

 possessed in ancient times, and to find as early as two hun- 

 dred years before the Christian era a very clear account 

 given of the tides at Cadiz. But the Romans generally, 

 knowing only the Mediterranean, had not much clear knowl- 

 edge of the tides. At a much later time than that, we hear 

 from the ancient Greek writers and explorers Posidonius, 

 Strata, and others that in certain remote parts of the world, 

 in Thule, in Britain, in Gaul, and on the distant coasts of 

 Spain, there were motions of the sea a rising and falling of 

 the water which depended in some way on the moon. Julius 

 Csesar came to know something about it; but it is certain 

 the Roman Admiralty did not supply Julius Caesar's cap- 

 tains with tide tables when he sailed from the Mediter- 

 ranean wi f h his expeditionary force, destined to put down 

 anarchy in Britain. He says, referring to the fourth 

 day after his first landing in Britain "That night it hap- 

 pened to be full moon, which time is accustomed to give the 

 greatest risings of water in the ocean, though our people 

 did not know it." It has been supposed however that 

 some of his people did know it some of his quarter- 

 masters had been in England before and did know but 

 that the discipline in the Roman navy was so good that they 

 had no right to obtrude their knowledge; and so, although 

 a storm was raging at the time, he was not told that the 

 water would rise in the night higher than usual, and noth- 

 ing was done to make his transports secure higher up on 

 the shore while he was fighting the Britons. After the 

 accident Caesar was no doubt told " Oh, we knew that be- 

 fore, but it might have been ill taken if we had said so." 



Strabo says "Soon after moonrise the sea begins to 

 swell up and flow over the earth till the moon reaches 

 Hid heaven. As she descends thence the sea recedes till 

 bout moonset, when the water is lowest. It then rises 

 again as the moon, below the horizon, sinks to mid heaven 

 under the earth." It is interesting here to find the tides 

 described simply with reference to the moon. But there is 

 something more in this ancient account of Strabo; he says, 



