I.] THE THAMES. 3 



toTeddington, though the distance between these two points 

 is less than twenty miles. It is almost needless to add that 

 this tidal action is of vast service to the port of London, 

 since barges, lighters, and other boats are thus enabled at 

 certain periods of the day to float up or down the river with 

 little or no expenditure of power on the part of the boatmen. 



Above Teddington Weir the motion of the river is 

 totally different from that which is observed at London 

 Bridge. There is no alternate backward-and-forward motion, 

 no regular rise and fall of the water, but the river flows 

 onwards in one constant direction, always running down 

 towards London. Careful observations at Teddington have 

 shown that, with the water at ordinary summer-level, about 

 380 million gallons^ flow over the weir every four-and-twenty 

 hours. This vast volume of water is swept down past 

 London, and ultimately carried out to sea. As the ebb- 

 tide runs for about seven hours, whilst the flood lasts only 

 five, it is clear that much more water runs down than flows 

 up ; and it is in this way that the vast volume of water 

 sent down from above Teddington drains away seawards. 



In seeking the origin of the water thus brought down 

 by the Thames, it is necessary to trace the river to what 

 is commonly called its " source." On ascending, it is ob- 

 served that the river grows smaller, the volume of water 

 becoming less and less. Thus at Teddington the Thames 

 is only 250 feet wide at high- water, whilst its M-idth at 

 London Bridge is about 800 feet. Following the many 

 windings of the river past Windsor, Reading, and Oxford, 

 we observe the stream still growing more narrow and 

 more shallow, until at Lechlade, in Gloucestershire, 146 

 miles from London, the Thames ceases to be navigable. 



1 Many of the statistical data relating to the Thames have been 

 obligingly furnished by Mr. l.each, of the Thames Conservancy Boatd. 



B 2 



