THE KING'S MIRROR 93 



things that I have brought up for discussion are subjects f .*..; 

 which especially touch the welfare of (seafaring menjand/ j 

 it looks to me as if they would profit much from a knowl- f 

 edge of these matters, since it gives insight into the / 

 right conduct of their profession. And since I intend to ) ' 

 labor diligently in the trader's callingJI should like very/ 

 much, if it can be done, to have you explain further some 

 of those things that I have just mentioned. 



Father. Those things that you have now asked about 

 do not all wax or wane with equal rapidity; for the tide, 

 when it rises, completes its course in_ seven days plus 

 half an hour of the eighth day; and every seventh day 

 there is flood tide in place of ebb. For the tide rises one 

 seventh part daily from the time when the rise begins; 

 and after it turns and begins to fall, it ebbs in the same 

 way during the next seven days but is retarded as much 

 as half an hour of the eighth day,* which must be added 

 to the seven days. As to how long an hour should be I 

 can give you definite information; for [there should be 7 

 twenty-four hours in two days, that is, a night and a V 

 day, while the sun courses through the eight chief points [ ^y 

 of the sky: and according to right reckoning the sun will j 

 pass through each division in three hours of the dayJOn / 

 the other hand, the moon, while it waxes, completes its 

 course in fifteen days less six hours; f and in a like period 

 it wanes until the course is complete and another comes. 

 And it is always true that at this time the flood tide is 

 highest and the ebb strongest. But when the moon has 

 waxed to half, the flood tide is lowest and the ebb, too, 



* The mean retardation is forty-eight minutes. 



f This is within twenty-two minutes of the length of the lunar half -month. 



