88 THE REV. W. WHEWELL'S RESULTS OF TIDE OBSERVATIONS. 



on the south coast enable us to reply, that the hours do follow an order of this kind. 

 Along a great extent of coast (from the Land's End to the Isle of Wight) the tide- 

 hours increase in order from 4^ 30™ to 1 1^ 30°^. But from the Isle of Wight eastward, 

 the tide-hour continues to be about 1 1^ 30™, with small and irregular changes only : 

 and this is true as far along the coast eastward as the observations have been reduced. 

 The examination of the eastern-coast observations will show how far this peculiarity 

 extends. 



Thus " the tides meet," in reality, along the whole coast, from the Isle of Wight to 

 the Downs, and perhaps to the coast of Suffolk ; that is, along the whole of this tract 

 the water is affected by the tide-waves which arrive in the two opposite directions. 



It may appear strange that the influence of the eastern tide should cease suddenly 

 when it reaches the Isle of Wight, not extending any further to the west. If, how- 

 ever, we look at the map, and observe the sudden widening^of the channel to the west 

 of Cape La Hogue, we shall be at no loss to conceive that the tide-wave may be ex- 

 tremely diminished by this rapid diffusion, as we know that the tides are greatly in- 

 creased by the gradual contraction of their beds in estuaries and rivers. But whether 

 or not this be the cause, the fact is indisputable in the observations, that to the east 

 of this point the tide-hour changes very little, while to the west it diminishes with 

 comparative rapidity. 



If it were at all doubtful that this difference arises from the interference of the 

 eastern tide as far as this point, the question would, I conceive, be settled by the two 

 following articles. 



9. The heights, as well as the times of high water, were observed ; these heights I 

 have hitherto examined for a particular purpose only, namely, to ascertain the ex- 

 istence of a diurnal difference of height, which follows from the theory, as I have ob- 

 served in a former paper *. From this examination it appears that this diurnal dif- 

 ference manifests itself with remarkable constancy along a large portion of the co^st 

 now under consideration. From the Scilly Islands to Portland Bill, most of the sta- 

 tions exhibit this inequality operating upon the greater part of the tides. The law is, 

 as is well known, that at a certain season of the year the morning tide is greater than 

 the afternoon tide, and at a certain other season it is less. In June the evening tide 

 was the greater; this appears clearly in the early part of the observations. As the 

 morning tide approaches noon, the difference diminishes ; and when the morning tide 

 is become the afternoon tide, the diurnal difference has skipped one tide, so as still to 

 be found conforming to the rule. The diurnal difference of height is variable, ranging 

 from two or three inches to one foot. 



10. I have said that this diurnal difference may be traced as far as Portland Bill. 

 Eastward from this point the tides do not appear to be affected by it, the morning 

 and evening tide not having any steady relation of greater or less. 



This change is remarkable, and the more so when we observe that it takes place 



* Philosophical Transactions, 1833, p. 221. 



