202 POPULAR LECTURES AND ADDRESSES. 



and tidal streams) throughout the British Channel 

 west of Beachy Head and St. Valery-en-Caux, do 

 not differ much from what they would be if the pas- 

 sage through the Straits were stopped by a barrier 

 between Dover and Cape Grisnez (Calais). 



3. A partial effect of the actual current through 

 the Straits is to make the tides throughout the 

 Channel, west of a line through Hastings to the 

 mouth of the Somme, more nearly agree with what 

 they would be were there a barrier along this line, 

 than what they would be if there were a barrier 

 between Dover and Cape Grisnez. 



4. The chief obviously noticeable effect of the 

 openness of the Straits of Dover on tides west of 

 Beachy Head is that the rise and fall on the 

 coast between Christchurch and Portland is not 

 much smaller than it is. 



5. The fact that the tidal currents commence 

 flowing westward generally an hour or two before 

 Dover high-water, and eastward an hour or two 

 before Dover low-water, instead of exactly at the 

 times of Dover high and low-water, is also partially 

 due to the openness of the Straits of Dover. 



6. The facts referred to in Nos. 4 and 5 are 

 no doubt partially due also to fluid friction (in 

 eddies along the bottom and in tide-races), and 

 want of absolute simultaneity in the time of high- 

 water across the mouth of the Channel from Land's 

 End to Ushant. Without farther investigation it 

 would be in vain to attempt to estimate the 



