128 jNIr. Lubbock on the Tides in the Port of London. 



therhithe church, as I slated in the Companion to the British 

 Ahnanac, but frequently from the clock of \^'^apping church, 

 which is close to the pier-head ; but this point is of no conse- 

 quence whatever. 



It may peihaps interest some of your readers whose notice 

 has been drawn to this subject, to see a comparison between 

 the calculation and the fact, as far as the time has yet gone. 

 M. Dessiou's calculations begin with the 1st of January : 

 thirteen days of that month only have now elapsed; and the 

 shortness of the time is of itself a serious obstacle to any ex- 

 act agreement of theory and observation ; for such an agree- 

 ment is to be looked tor only in mean results deduced from 

 many comparisons. The accidental causes which influence 

 particular tides are so many and so obscure, and tiie mode of 

 observation so inexact, that I do not conceive that either these 

 tide-tables, or any other, can be free from deviations from the 

 noted time, which may often amount to a quarter of an hour. 

 It appears by the following register and calculations, that, as 

 far as the observations have yet been made, the mean time of 

 high-water at the London Docks has differed by less than four 

 minutes from the tables in the British Almanac. 



I am well aware that the practical application of this subject 

 requires considerable caution, and that the observations which 

 it would be desirable to make, are by no means so simple 

 as might at first be imagined. The difficulty arising from the 

 insensible change of the height of the tide just at the maximum, 

 which produces what is called the hanging of the tide, is of an 

 obvious nature. It may not perhaps be so obvious that the 

 rise and fall before and after the maximum are by no means 

 symmetrical ; but this I understand from Captain Eastfield is 

 the case, under whose superintendence a most valuable series 

 of observations has been undertaken at the East India Docks, 

 but which are not likely to be continued for any great length 

 of time. In a country like ours, where both from scientific 

 and commercial considerations the subject of the tides is so well 

 worth attention, it is not too much to hope for the assistance 

 of Government in procuring at least one series of accurate 

 observations continued for many years. 



When the mode of observing the time of high-water has been 

 rendered as accurate as it ought to be and might easily be 

 made, and when a series of observations have been made on 

 such an improved plan, we may endeavour to introduce greater 

 exactness into our tables ; but at present the agreement is 

 more than sufficient for practical purposes, and the mean error 

 is within the limits of the errors of the observations. 



Com- 



