208 REPORT ON THE SURFACE DRIFT OF THE ENGLISH CHANNEL 



duratiou was prolonged to 22 days (assuming here, as elsewhere, that the 

 bottle was picked up soon after getting ashore), thus depriving the case 

 of any special significance. 



The only period of marked southward drift which is actually indicated 

 by the bottles was in the month of May, when — between the loth and 

 the 19th of the month — as many as five bottles, belonging to four 

 February batches, were stranded on the French coast in the neighbour- 

 hood of Calais. It is clear also, from evidence supplied by batches 

 XXXVIII. and XL, that similar conditions prevailed at the opposite 

 extremity of the Channel during the same period, which was char- 

 acterised, as already remarked, by a preponderance of north-westerly 

 winds in the Channel. 



The only other month during which northerly winds prevailed was 

 January, and I have already mentioned that the negative evidence sup- 

 plied by the non-recovery of bottles in February, in spite of strong 

 southerly winds during that month, points clearly to the conclusion that 

 a strong southward drift occurred in January as well. 



A temporary southward drift probably occurred also about the middle 

 of June, at any rate in the eastern portion of the Channel, since two 

 bottles, belonging to different batches, stranded at Calais and Boulogne 

 on the 18th and 19th of that month. It is, moreover, difficult to account 

 for the curious data supplied by batch no. XL, except by the assumption 

 that there was a surface current to the southward on the north coast 

 of Cornwall between the middle of June and the middle of August, and 

 again during September. These were periods of variable winds. 



§ 3. Other Causes of Surface Currents in the Channel. — By the use 

 of the word " drift " in connection with the movements of the surface 

 water which have been described above, I have already indicated that 

 these movements are principally due to the driving power of the wind 

 exerted upon the surface of the water, M}' employment of the word 

 is amply justified by the close correspondence between the movements 

 of wind and water in the Channel revealed in the preceding section of 

 this report. But it is desirable, before' we assume that the local winds 

 have been the only factors concerned in the production of these surface 

 currents, that we should consider for a moment the other causes which 

 may be expected to affect the circulation of the water in the regions 

 under discussion. 



In the first place we have to entertain the possibility of a current 

 setting normally through the Channel, independently of the local 

 winds, in connection with the general circulation of Atlantic water. 

 As the Channel is open to the eastward through the Straits of Dover, 

 we might, a iiriori, expect a continuance through it of the great east- 

 ward drift of the North Atlantic. Into the Bay of Biscay this drift 



