490 FOURTH REPORT — 1834. 



the filling up and raising the bed by depositions of gravel and 

 mud; — that independently of the annual loss of lives and pro- 

 perty, occasioned by the contracted waterways of the bridge, 

 the navigation was at times wholly impeded ; whereas, by re- 

 moving the dam, the great increase in the velocity of the current 

 would clear the bed of the I'iver, facilitate navigation, and effect 

 a more perfect drainage of the country by the quicker passing off 

 of the land-floods ; — that the river being more perfectly emptied 

 at each reflux, the flux would have less time to fill the increased 

 void ; and that, therefore, before it had attained its greatest sur- 

 face of elevation, the tide would have begun to run down ; — that 

 although many shoals would have undoubtedly been exposed, 

 yet the increased velocity of the current, assisted by dredging 

 the hard places, Avould very soon reduce the channel to its ancient 

 depth. The latter assertions have been verified to their full ex- 

 tent, as will be seen hereafter. 



The phsenomena of the tides in the port of London have been 

 very ably discussed by Mr. Lubbock and by the Rev.Mr. Whewell 

 in the Philosophical Transactions ior \h& years 1831, 1833, and 

 1834, — the former gentleman in his papers containing numerous 

 tables compiled from 13,073 observations made at the London 

 Docks in a period of nineteen years, viz. from January 1st, 

 1808 to the 31st of December, 1826, with the corrections for 

 the time of high water, as it is affected by the right ascensions, 

 declinations, and parallaxes of the sun and moon ; and the latter 

 in his paper on the empirical laws of the tides in the port of 

 London, and in his essay towards a first approximation to a map 

 of cotidal lines. 



In the case of the times of high water especially, says Mr. 

 Whewell, " the general course of the variations of the quan- 

 tities is as regular as can be expected, and as is reqiiisite for 

 my formulae. The heights are much more anomalous ; pro- 

 bably they are more affected by winds, &c. than the times are : 

 and when we reflect that the tide at London may be affected by 

 the operation of causes in a remote part of the ocean, propa- 

 gating their effect by the progression of the tide-wave, we shall 

 not be siu'prised at considerable deviations from the rule. The 

 trade- winds and other winds of the tropical regions may be felt 

 in our tides, and may even affect the means of long series of 

 observations ; for it is to be recollected that the averages which 

 we obtain are not the averages of the effects of the sun and 

 moon alone, but the averages of their effects, together with that 

 of meteorological causes. 



" It is moreover to be observed, that the peculiar circum- 

 stances of London in having a tide compounded of two tides 



