314 Proceedings of the Royal Physical Society. 



the direct track of migrants, and a very short distance north 

 of the parallel of latitude of Heligoland. The distance to 

 the westward being considerable, it is the more easily under- 

 stood why certain species which cross over Heligoland do 

 not, or only very rarely do, reach either the Isle of May or the 

 east English coasts, but make their turning-point somewhere 

 about Heligoland, and probably follow the old submerged, 

 and the presently elevated valley of the Khine, of which 

 formerly all the rivers of England, south of Spurn Point and 

 the Dogger Bank, were tributaries before the submergence 

 took place, as well as all the rivers of Belgium, Holland, and 

 Prussia flowing northwards. The Isle of May appears to me 

 to be the northern limit (along with the Bell Kock and part 

 of the Forfar coast) of the influence of migratory waves 

 which cross Heligoland. Because in northerly and westerly 

 winds migration at Isle of May is represented by a " closed 

 fan," and by throbs and rushes ; whereas, south of Spurn 

 Point, the whole English coast is visited equally, whether 

 the wind is a little northerly or not. Of course, much 

 heavier returns occur with S.E. winds at all east coast 

 stations. The migratory waves observed at Pentland Skerries 

 we consider are not closely connected with the waves of those 

 observed at Heligoland and Isle of May, but I shall not en- 

 large upon the position of the Pentland Skerries at present, 

 as there is subject enough there to form a separate paper. 



3. Let us now speak, in the third place, of the present 

 aspects of the Isle of May and its lighthouse. 



The Isle of May lies in a nearly north and south position 

 across the entrance of the Firth of Forth, and is about one 

 mile in length by a quarter of a mile in breadth, having a 

 superficial area of about 240 acres, as shown upon the six- 

 inch scale map of the Ordnance Survey. The highest parts 

 of the island are 250 feet above sea-level, and on one of these 

 stands the massive and handsome castellated structure of the 

 lighthouse, the lantern of which is 270 feet above the sea, 

 and the top of the dome some 14 feet or so higher than the 

 centre of the lens.^ A little to the east of the lighthouse, 

 on the other side of a hollow, but nearly on the same level, 



^ The principal lighthouse was erected in 1816. 



