WHAT IS THE TIDE OF THE OPEN ATLANTIC? 469 



the general course of a tidal wave advancing up the Atlantic at 

 least as far as Gibraltar. 



Dr William Whewell took up the investigation in the thirties. 

 From all the charts, sailing directions, and ocean pilots he could 

 obtain, he computed cotidal hours for points all over the world, 

 being the time of high water on the day of new or full moon. 

 From these data he traced the progression of the tide up the 

 Atlantic to the coasts of Europe and America, deriving it from 

 the belt of ocean to the south. He published his cotidal chart 

 in 1833.* He was fully conscious of the very crude data given 

 him at times by observers who fancied the tides always occurred 

 at the same hour, and he closedhis first essay with the warning 

 that the results were only tentative. Figure 1 reproduces the 

 Atlantic portion of this chart. 



Dr Whewell was moved by this lack of good data to seek the 

 cooperation of the admiralty to have careful observations made 

 simultaneously at least about .the British shores. He not only 

 accomplished this, but was enabled in 1835 1 to publish obser- 

 vations made according to his instructions at 666 stations in 

 America and Europe, with two at the Cape of Good Hope, for 

 every tide between the 8th and 28th of June of that year. The 

 greater part of these were about the British isles, and for this 

 region he published a revision of his chart. For the American 

 coast he contented himself with pointing out some errors in his 

 first chart. The rest of the chart he abandoned until a wide 

 range of good observations should be at hand. 



DIFFICULTIES OF THE EARLIER VIEW 



Now defects in the general scheme of cotidals are defects in 

 the theory of a wave progressing up the Atlantic from the south. 

 These defects Whewell found to be based on (1) the extraordi- 

 nary manner in which the cotidals contour about the lands, 

 together with the difficulty of including the oceanic islands in 

 the system, and (2) the great difference of epoch of the diurnal 

 wave in Europe and America, together with the identical epoch 

 in Spain and at the Cape of Good Hope, supposed to be sepa- 

 rated by a long journey up the Atlantic. 



* Phil. Trans., 1833, p. 147. This chart is reproduced in numberless excellent works, 

 though abandoned by its author in the first two years of its existence, and it is usually 

 reproduced, even in America, without the correction the author indicated for the xiih. 

 line on our coast. Thus in Young's General Astronomy, for instance, 1889, p. 287. 



fPhil. Trans., 183G, p. 289. 



