Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

278 APPENDIX. bore the unpretending title of an " Essay towards a first approxima- tion to a Map of Cotidal Lines;" but however Hghtly 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. WheweU 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 generalized." * 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 lide ; and in this manner have arisen such anomalies as have been mentioned." And again : I " 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. I Ibid.