MELANISM AND MELANOCHIIOISM. 51 



to the prcvailinj^ south-west winds, and so help to counteract 

 and modify the influence of the latter. 



Now let us combine Nos. 2 and 3 above. The moisture 

 which has been obtained by the south-west winds in their 

 passage across the Gulf Stream is driven by them over 

 our western shores. The air has to rise to cross our hills and 

 mountains, and falls as rain. As the wind comes on, it loses 

 more and more of its moisture, until, by the time it reaches 

 our eastern shores, the quantity of moisture is comparatively 

 small. Hence we find that the west coasts of our Islands 

 have excessive annual i-ainfalls — sometimes from 70 to 80 

 inches — whilst the average of the south coast is less than 20. 

 Not only is the rainfall of our west coasts heavy, but the air 

 is much more humid than that of the east. 



But it must not be supposed that the climate of the east 

 coast is not modified at all by the Gulf Stream. The humidity 

 of the air on the east coast is much greater than on the Con- 

 tinent, where the prevailing winds are east or north-east, and 

 even the easterly winds are slightly less dry than when they 

 cross the Continent, as the North Sea, narrow as it is, has 

 some little effect in modifying them in this way. 



Summarising the result, we find— (i). That North and North- 

 western Scotland and Ireland are the most humid districts in 

 Britain ; Eastern and Southern Scotland, North-western 

 England and Wales following ; the Midlands next ; and the 

 South and Eastern parts of England least humid of all. (2). 

 That our least humid areas are much more humid than 

 areas in corresponding latitudes on the Continent, and all 

 high-lying areas have a greater rainfall than low-lying areas 

 in the same districts. 



I would now direct attention to a few facts relative to the 

 distribution of melanism in this countr}-. 



Mr. Percy Russ has shown us that a very great number ol 

 remarkable cases occur on the west coast of Ireland. At 

 Sligo a very large number of species are melanic, and probably 

 this is more noticeable among the Noctu-'E than any other 

 group. The greater part of Ireland is comparatively un- 

 worked. Collectors have from time to time stayed at different 

 places, and have at various times compiled lists of the different 

 species that have come under their notice, but this method 

 fails almost entirely in giving us scientific results. The 

 energy of our professional collectors has opened up to us the 

 wonderful melanic variation so frequent in the Hebrides and 



