1882.] 



President's Address. 



already published by them in 1871. The charts now embody 

 the results of observations extending over a period of twenty-four 

 years; the revised edition, as well as the original publication, are due 

 to the indefatigable activity of Mr. Alexander Buchan, F.R.S.E., 

 the Secretary of the Scottish Meteorological Society. An atlas of 

 convenient size, intended for the use of observers in the United 

 Kingdom, and conveying similar information derived from data partly 

 different, and quite independently discussed, has been already pre- 

 pared by the Meteorological Office, and will immediately appear. 



It is a fact now universally recognised that the greater part of the 

 changes of weather which are experienced in the British Isles are 

 occasioned by travelling areas of excessive or defective atmospheric 

 pressure, which arrive at our shores from the Atlantic Ocean. The 

 importance of a systematic study of the weather of the North 

 Atlantic being thus indicated, the Meteorological Council have 

 resolved to undertake the preparation of synoptic weather charts for 

 the thirteen months beginning 1st August, 1882, and ending 31st 

 August, 1883, and have issued a special appeal to the British shipping 

 interest for active co-operation during that period. It is satisfactory 

 to know that this appeal has not been fruitless, and that there is 

 every prospect that the number of observations available for the dis- 

 cussion will exceed 200 per day. 



This is, perhaps, the proper place to make mention of some results 

 having an important bearing on meteorology, obtained by Professor 

 Tyndall in the course of a larger research on the action of radiant heat 

 on gases, 



By methods which he has applied to gases and vapours generally, 

 Tyndall has established anew the action of aqueous vapour upon 

 radiant heat, and the sensibly perfect diathermancy of dry atmo- 

 spheric air. The phenomena of solar and terrestrial radiation are 

 profoundly modified by the presence of aqueous vapour in the earth's 

 atmosphere, the temperature of our planet being thereby rendered 

 very different from what it would otherwise be. 



The celebrated experiments of Patrick Wilson, wherein were 

 observed a rapidity of radiation and a refrigeration of the earth's 

 surface previously unknown, are explained by the fact that when 

 they were made the amount of aqueous vapour in the air was in- 

 finitesimal, the unhindered outflow of heat towards space being 

 correspondingly great. The sagacious observation of Six and Wells, 

 that the difference between the surface temperature and that of the 

 air a few feet above the surface, on equally serene nights, is greatest 

 in cold weather, is explained by the fact that, when the temperature 

 is low, the agent which arrests the surface radiation is diminished in 

 quantity. Wells, moreover, found that the heaviest dews were 

 deposited on nights when the difference between air temperature and 



