I 



367 



On the probable importance of Tide Observations at the 

 Cape of Good Hope. By the Rev. W. Whevell, 

 Fellow of Trinity College, Cambridge. 



rcommunicated by Sir John Herschem., Bart., President of the 

 South African Literary and Scientific Institution, and read on 

 Gth May, 1835.] 



1 It appears to be (luite certain, from the general course of 

 the times of high water on the shores of the Atlantic, that the 

 tide comes to Europe from the Southern Ocean. For the 

 tide hour on any day is later and later as we proceed from the 

 Cape of Good Hope along the shores of Africa, bpani, 

 Ffance,- and England. Therefore, considering the matter 

 merely in this general manner, it would be very desirab e to 

 know the exact time of high water at the Cape, that we know 

 how long the tide wave (for the tide may be imagined travelling 

 like a vast wave) takes to travel from the south point of Africa 

 to any part of Europe. . . r 



2 The tide wave employs about 24 hours in moving from 

 Cape Town to London. But it maybe asked where does it 

 come from, to Gape Town? What ,s Us ^"th-place ? fo 

 answer this question, as far as it admits of an a"«;^<^'' '^ "J"^ «f 

 the objects for which good tide observations at the Cape aie 

 very desirable. But this requires some explanation. 



If the tide employs 24 hours in going from the Cape to 

 London, it must at London be 24 hours older than it was at the 

 Cape. But what indication have we how old the tide is? 

 We have two such indications: I will explain them in order. 



3. The highest spring tide corresponds to the full and new 

 moon ; but it does not happen on the day of full "L^^w moon ; 

 it happens a day or two or three days later Why is this ? 

 AppaJently it is, because the tide has employed a day, or t^v^ 

 fAhree dlys, in getting from the place when it was born to the 

 place wben it is%bserved. The greatest tide is born on 

 Monday the day of the full moon, in the Southern Ocean ; 

 but tlS'g eatestlide does not reach London till Wednesday or 

 Thursday two or three days after the full moon. And thus 

 Te WghJs't spring tide is always some days after the new or full 



"™'stltn\"s::rpiausible: but if it be true, the greatest 

 spring tfde must arrive at the Gape a day sooner then it arrives 

 a? Lo^ndon. If the highest tide happen at London on Wed- " 

 dav it must happen at the Cape on Tuesday. It at London it 

 be dwa; two da'ys after new or full moon, at the Cape it must 

 be always one day only after that occurrence. 



