Royal Physical Society. 15 



from water. Similar slags were exhibited by Professor Fleming from 

 Maryculter, Aberdeenshire. An accurate analysis of the mineral was re- 

 commended, and a report to be given in to the Society at its next meeting. 



II. Contributions to the Hydrology of the British Islands. By William 



Rhind, Esq. 



The peculiar position of the British Islands, in the great trough of the 

 North Atlantic, by which they are brought within the influence both of 

 the Gulf Stream and of the equatorial air currents, has a marked effect 

 in modifying their climate. By both these influences the winter tempera- 

 ture is greatly mitigated, in comparison with that of the corresponding 

 parallels on the Continent of Europe and Asia, while the intensity of the 

 summer heat is also tempered by the surrounding ocean. For fully two- 

 thirds of the year the prevailing winds in Britain are the south, south- 

 west, and north-west. The south-westerly winds are predominant from 

 June to the end of December, while the easterly current prevails from 

 March to the end of May. The southerly winds originating in the tropics, 

 and blowing over the Atlantic Ocean, whose temperature is kept up by 

 the influence of the Gulf Stream, are of elevated temperature, and highly 

 charged with moisture. The north-easterly winds, on the other hand, 

 coming from circumpolar regions, and blowing over a long tract of con- 

 tinent, are chill and dry. To the contact and opposition of those two cur- 

 rents then, as is well known, we owe to a considerable extent our rainy 

 weather ; the cold east wind becoming the condensing agent. But we shall 

 find that besides the north-easterly currents there are other condensing 

 agencies constantly at work. 



In collecting materials for the Hydrology of the British Isles, in con- 

 nection with Mr Keith Johnston, for the second edition of his Physical 

 Atlas, the author had obtained, from published and unpublished sources, 

 upwards of one hundred records of rain stations and temperature. These 

 amounts were marked down in their respective positions on the map of 

 Britain, and this map was coloured with light and dark shades according 

 as the amount of rain- fall was small or large in the locality. The map he 

 exhibited showed, in the first place, what had been already done, and what 

 parts of the country yet remained to be filled up by observation and re- 

 gistration. A considerable portion of the surface of Britain and Ireland 

 was observed to be dotted with figures, but a large part of Wales and the 

 north-west coast of Scotland were deficient. If we take three waving lines 

 along the map of Great Britain we shall meet with three gradations of 

 rain-fall. The line along the east coast, and penetrating some way into the 

 interior, marks out the region of least deposition. On the whole eastern 

 side of England, from Kent and Surrey, and Oxford, north to York, the 

 average annual fall of rain is 23 to 24 inches. From Durham, north into 

 Scotland, the mean fall is 27 inches, though in some localities, as Mid- 

 Lothian and Morayshire, the rain-fall is from 24 to 25 inches. The mean 

 annual rain-fall of the whole eastern half of Great Britain is 27 inches. 



