xviil INTEODUCTIOIir. 



of Ireland is a little over 50° Fahrenlieit, wMcli ia about the 

 same average aa in south Britain. But itia not the mean tempera- 

 ture of any country so much as the extreme ranges, which affect in 

 Summer the ripening of fruit and crops, and in Winter the preser- 

 vation of tender plants. There is a striking difference between 

 Ireland and Great Britain in this respect, for the mean temperature 

 of the Summer months being 2° (Fahrenheit) lower in Ireland, the 

 ripening of com and fruit is later and more uncertain than in 

 England, and wheat, which is cultivated successfully throughout 

 neariy all England, is in many parts of Ireland a precarious crop, 

 especially in the western counties. The Spanish chestnut, walnut, 

 and fig seldom fully ripen their fruit. On the other hand, 

 the Winter temperature being about 2° higher in Ireland, some 

 plants thrive and flourish with us which would be killed by the cold 

 dry frost of an English Winter. Even in the county of Dublin, 

 some species which are natives of the western coast of Ireland are 

 occasionally unable to bear the Winter when planted out in the open 

 air in the Botanic Garden at Glasnevin; for example, Simethis 

 bicolor, and the small form of Statice occidentalis, from Arran, Erica 

 •ciliaris, and E. Mackayi, suffer much from frost at Glasnevin. 



The temperature of Ireland decreases from south to north at the 

 'rate of about three-quarters of a degree for each degree of latitude^ 

 A sensible decrease is also experienced from west to east, especially 

 in Winter, when the effects of the Gulf Stream are most felt. It 

 is, indeed, to this vast body of, heated water that Ireland owes 

 its milder Winter; and as the prevailing winds blow principally 

 from the south-west, they have also great effect in moderating the 

 climate. In the course of the experiments conducted by Dr. 

 Lloyd and others in 1851, it was found that the temperature of the 

 sea off the west coast of Ireland exceeded that of the air on laud— 

 the difference amounting to 1°'8 in Summer, and 5°'7 in Winter. 



Besides warming the air, the Gulf Stream renders it more humid, 

 as is proved by the rain-fall being much greater in the west than 

 in the east. Dr. Lloyd has calculated the average amount of 

 saturation at 90 per cent, on the west, and 85 per cent, on the east 

 coast. This vapour-laden air being carried inland by the prevail- 

 ing south-westerly winds, as soon as it reaches the mountains is 



