220 REPORT ON THE SURFACE DRIFT OF THE ENGLISH CHANNEL 



northward, but of small value (3'). The disturbing effects of Portland 

 Race perhaps account for this slight discrepancy ; but a closer estimate 

 would probably have been obtained by taking the mean between the 

 Prawle Point and Ptousdon winds. During March, when the state of the 

 wind was very similar to that in February, I found that the records at 

 Rousdon indicated a stronger component from the northward than did 

 those at Prawle Point. 



The six succeeding cases deal with batches all of which were repre- 

 sented in the neighbourhood of Calais by bottles recovered between 

 the 13th and 19th May. They are, therefore, of particular interest as 

 throwing light on the whole course of drift. There is a glaring dis- 

 crepancy between the estimated and actual drift of the Seaford bottle 

 (VII. 1); but the remainder conform moderately well, especially when 

 the length of the journeys involved is taken into account. From the 

 close correspondence between estimated and actual drift in cases IX. 1 

 and 2 we may, I think, conclude that the inferences to be drawn from 

 the use of the drift-factor in all these cases are reliable. In the Seaford 

 case there is an angular error of 8°, a distance error of 41 miles, and a 

 serious geographical discrepancy of position. Had there been open 

 water in the estimated direction of drift, the Seaford bottle should have 

 been on the east coast of Sheppey on April 17th. We see, however, 

 from IX. 1 that these bottles, which from their eventual destination we 

 may shortly term the Calais bottles, were off the south coast of the Isle 

 of AVight about March 16th, and so violent were the westerly gales of 

 the latter half of March that the estimated drift during that period was 

 120 miles in a N.E. by E. direction, which would bring the bottles to a 

 position 5 or 6 miles E.N.E. of the Nore Lightship off the mouth of the 

 Thames. The Sussex coast, however, would interpose an impassable 

 barrier to such a course, and two alternatives would present themselves: 

 (1) the bottles must drive at once ashore, or (2) the bottles must be 

 deflected from their estimated course by a current racing eastwards along 

 the shore towards the Straits of. Dover. The latter course appears 

 to have been taken in most cases, and the bottles were probably in the 

 lower part of the North Sea, between the Essex and Belgian coasts, at 

 the end of the month. That the passage of the Straits was made at 

 this time in spite of the southerly component in the winds is rendered 

 all the more probable because a bottle of batch II., which was off the 

 coast of Eastbourne on March 16th, was recovered at Terschelling on 

 March 30th. This is equivalent to a distance of 250 miles in 14 days, 

 or almost 18 miles a day. Now the estimated drift, directly dependent 

 on the pressure of the wind during this period, was 120, or at most 140 

 miles. This velocity was therefore nearly doubled, no doubt partly 

 owing to the head of water accumulated in the eastern part of the Channel 



