278 



APPENDIX. 



bore the unpretending title of an " Essay towards a first approxima- 

 tion to a Map of Cotidal Lines ;" but however lightly the author 

 might esteem it, there can be no doubt that it tended to remove a 

 cloud which hung over numerous difficulties ; and to enable us not 

 only to take a general view of them, but to see how we should direct 

 our course in order to attain some knowledge of their intricacies. 



In 1831 Mr. Lubbock called the attention of mathematicians, as 

 well as of practical seamen, to the subject of Tides : but it was Mr. 

 Whewell who aroused general interest ; and, assisted by the Admi- 

 ralty, engaged the co-operation of observers in all quarters of the 

 globe. 



At the first perusal of Mr. Whewell's essay, I was particularly 

 struck by the following passages : " But in the meantime no one 

 appears to have attempted to trace the nature of the connexion 

 among the tides of the different parts of the world. We are, per- 

 haps, not even yet able to answer decisively the inquiry which 

 Bacon suggests to the philosophers of his time, whether the high 

 water extends across the Atlantic so as to affect, contemporaneously, 

 the shores of America and Africa } or, whether it is high on one side 

 of this ocean when it is low on the other ? at any rate, such obser- 

 vations have not been extended and generahzed." * Also : f 



" If the time of high water at Plymouth be five, and at the Eddy- 

 stone eight (as formerly stated), the water must be falling for three 

 hours on the shore, while it is rising at the same time at ten or 

 twelve miles distance ; and this through a height of several feet. We 

 can hardly imagine that any elevation in one of the situations, should 

 not be transferred to the other in a much shorter time than this. 



*' There is, in fact, no doubt that most, or all the statements of such 

 discrepancies, are founded in a mistake arising from the comparison 

 of two different phenomena ; namely, the time of high-water, and 

 the time of the change from the flow to the ebb current. In some 

 cases the one, and in some the other of these times, has been 

 observed as the time of the tide ; and in this manner have arisen 

 such anomalies as have been mentioned." And again : X 



" The persuasion that, in waters affected by tides, the water rises 

 while it runs one way, and falls while it runs the opposite way, though 

 wholly erroneous, is very general." 



These, and other valuable remarks, showed me what indistinct or 

 erroneous ideas I had entertained ; and that many other seamen had 

 * Philosophical Transactions, 1833, p. 148. t Ibid. 157. t Ibid. 



