AND NEIGHBOURING SEAS DUEING 1897. 211 



tide to the south-westward and of the West Channel stream to the 

 south-eastward, there is a strong convergence towards the French 

 coast between Dieppe and Boulogne. I have not, however, examined 

 minutely the effects of the Dover tides upon any of our drift-bottles 

 on the present occasion. The general occurrence of a southerly com- 

 ponent in the Channel winds renders it probable that most of our 

 bottles entered the Straits on the English side, where the net resultant 

 of the tidal influences appears to be in the same direction as the 

 prevalent winds, whose drift they would merely reinforce. In the case 

 of Mounts Bay, as already pointed out, the stronger currents are in the 

 opposite direction. 



The influence of the tidal indraught towards Boulogne possibly 

 accounts for the fact tliat the only bottles recovered on the French 

 coast west of Calais were found at Le Portel, near Boulogne — one on 

 June 19th, the other on August 5th (batches XX. and XXII.). 



The strong tidal currents at the entrances to the Gulf of St. Alalo 

 may have to be considered in future reports; but as only one batch of 

 our bottles approached this region last year, it does not appear to be 

 profitable to discuss their course on the present occasion. 



In Lyme Bay, however, partly owing to the conformation of the coast 

 line, and partly to the indraught of the great tides in the Gulf of St. 

 Malo, the tidal currents are very weak, and, instead of a parallel ebb 

 and flow in the northern part of the bay, the tidal stream in this 

 position is rotary in direction, changing, with the hands of a clock, 

 "round the compass, with little or no velocity." The slight velocity 

 of this vortex, compared with that due to wind-action, enables us to 

 neglect its effects upon the surface drift under ordinary circumstances. 

 But on the eastern side of the bay a stream runs to the south-eastwards 

 for nine hours out of the twelve, after apparently making the circuit of 

 the bay from the Start to Portland. Off Portland Bill the well-known 

 " Pace " is due to a combination of this outset from the bay, which has 

 gradually increased in velocity along its course, and a counter-stream 

 from East Portland Bay which sets for 9^ hours. In N. winds the race 

 extends nearly two miles from the Bill, with great overfalls beyond 

 that distance ; but with S. winds it scarcely exceeds half a mile. The 

 velocity of the race at springs is six or seven knots. 



It is clear that drift-bottles in the eastern part of Lyme Bay will tend 

 to the southward, independently of the winds, as a direct result of the 

 tidal currents here. In the western part of the bay they are not only 

 protected from the direct action of westerly and south-westerly winds, 

 but as a result of the slow tidal vortex tend to be carried north- 

 wards and then eastwards with the stream which sets to Portland. 

 It is a remarkable fact that only two of our bottles were recovered 



