56 Professor Barlow on the Tides 



The tabulated observations, from which the above abstract 

 has been made, were taken by Mr Pullman, superintendant 

 master at Woolwich Dockyard, and may be confided in for their 

 accuracy. They were taken at about mid-tide with a ship's 

 log, and with every possible care and attention. 



The following experimental results, as to the velocity at 

 ebb-tide above bridge, were furnished by Mr Jessop, civil en- 

 gineer. The velocity was ascertained by throwing into tlie 

 stream turnips and potatoes every 10 minutes for 45 minutes 

 during low water, in the middle, and on each side, of the river. 

 The greatest velocity thus deduced, was 21 feet in 517 se- 

 conds or about 2 J miles per hour, and the mean of each series 

 gave as follows : 



Near the London shore, 21 feet in 8.4 seconds. 

 In the middle, . . 21 6.5 



Surry side, ... 21 9.3 



General mean, 21 8.1 



Or 1| miles per hour nearly. 



6. — Line of High and Low Water. 



The mean low water-line has a fall of 12 inches between West- 

 minster and London Bridge, and from London Bridge to the 

 London Docks at spring-tides, a fall of 3 inches ; at neap-tides, 

 2 inches. Mean 2 J inches. 



The high water-line has a fall, in the contrary direction, from 

 London Docks to London Bridge, of IJ inch at spring- tides, 

 but it is a dead level at high-water neap-tides, as it is also be- 

 tween the London Docks and Blackwall. And from London 

 Bridge to Richniond the high water-mark is, according to the 

 survey of Mr Giles, the city surveyor, one dead level ; and this 

 gentleman informs me, that he has found the same circumstance 

 to obtain in several tide rivers ; although the Severn and some 

 others observe very different laws. 



7. Experiments to ascertain the Velocity of the general body of 

 Waters of the Thames. 



As the velocity, found as above, was obviously that of the 

 surface of the water, I thought it desirable to ascertain whether 



