496 



FOURTH REPORT — 1834. 



The following observations were made in March 1833 : 



The difference in time of high water at London ) 

 Bridge after that at Sheerness J 



The rise of tide at Sheerness 



Fresh Wharf. 



New London Bridge , 



The fall through the site of Old London Bridge 



The difference of level of High-water mark at Lon- "I 



don Bridge above that at Sheerness / 



The difference of level of Low-water mark at Fresh ) 



Wharf above that at Sheerness / 



March 6. March?. March 8. 



h. in. 



1 34 



ft in. 

 18 3 



18 1 

 2 5 



1 42 



ft. in. 



18 11 



20 8 



18 6 



2 2 



2 7 



10 



h. m. 



1 36 



ft. in 



18 7 



19 10 

 18 3 



1 7 



2 9 

 1 7 



N.B. — The above levels are from the Trinity datum as transferred from Lon- 

 don Bridge to Sheerness by Captain Lloyd. 



Observations and Experiments nputi the P'elociti/ of the Tides 

 of the River Thames. 



The earliest experiments on this subject with which we are 

 acquainted are those of Mr. H. Saumarez, inserted in the Phi- 

 losophical Transactions iox the year 1720, " On the strength 

 and gradual increase and decrease of the Tides of flood and ebb in 

 the river Thames, as observed in Lambeth Reach, off Manches- 

 ter Stairs, and in the middle of the river, with anew instrument 

 called the Marine Surveyor, on the 9th and 18th of June 1790, 

 both with spring and neap tides." 



These experiments are interesting, as showing the effect of 

 Old London Bridge on the river previously to the alteration of 

 the bridge and enlargement of the waterway in the year 1754. 



Mr. Saumarez's tables indicate the depth and velocity of the 

 floods and ebb of spring and neap tides for every fifteen minutes, 

 and the following are the results : 



hrs. min. 



The time of flood spring tide was only 3 50 



Ditto .... ebb ... . ditto 8 40 



Ditto .... flood neap ditto 4 50 



Ditto. . . . ebb .... ditto 7 35 



miles per hour. 



The greatest velocity in flood spring tides was .... 2-00 



Ditto ebb ditto 1-61 



Total number of miles run by the flood spring tide . . 5*25 



Ditto ebb 10-50 



The greatest velocity in neap tides was 1*44 



Ditto, with ebb of neap tides 1*30 



The total distance run with a flood of neap 4*75 



Ditto, vnih. an ebb of ditto 7*75 



