A MONTH ON THE EDDYSTONE 303 



fixed point of observation on the gallery I was enabled to 

 gauge the height from which these birds dived with a 

 degree of accuracy not usually attainable. I witnessed 

 many thousands of dives, but in no case did the drops 

 exceed a height of from 130 to 140 feet. About one- 

 fourth of the Gannets seen were in immature dress, all 

 stages being represented except that of birds of the 

 year. 



The Eddystone was an excellent station for studying 

 the weather conditions and their bearing upon bird- 

 migration. 



Birds when performing long flights not unfrequently 

 pass from the zone of favourable weather, which is 

 conducive to their departure, to an area in which the 

 conditions are more or less unfavourable ; and they are 

 consequently recorded as arriving on our coasts in the 

 autumn under adverse circumstances. Such inauspicious 

 instances of immigration as these are apt to mislead 

 those interested in the subject, for it is not always borne 

 in mind that it is the state of the weather at the point of 

 departure which affords the only true indication of the 

 actual conditions controlling the movements. 



At the Eddystone, owing to its contiguity to the 

 mainland, one witnessed the movements and could 

 simultaneously ascertain the meteorological conditions 

 under which the birds elected to set out on their passage 

 southwards. If no movements took place, either by day 

 or by night (other conditions being favourable for the 

 observation of night movements), then it was possible, 

 it being the height of the emigratory season, to deter- 

 mine what in all probability the weather-barriers were 

 which deterred the travellers from setting forth. Thus 



