1883.] 



On Terrestrial Radiation. 



21 



February 8, 1883. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



The following Paper were read : — 



" Note on Terrestrial Radiation." By John Tyndall, F.R.S. 

 Received February 5, 1883. 



On Hind Head, a fine moorland platean about three miles from 

 Haslemere, with an elevation of 900 feet above the sea, I have 

 recently erected a small iron hnt, which forms, not only a place of 

 rest, but an extremely suitable station for meteorological observations. 

 Here, since the beginning of last November, I have continned to record 

 from time to time the temperature of the earth's surface as compared 

 with that of the air above the surface. My object was to apply, if pos- 

 sible, the results which my experiments had established regarding the 

 action of aqueous vapour upon radiant heat. 



Two stout poles about 6 feet high were firmly fixed in the earth 

 8 feet asunder. From one pole to the other was stretched a string, 

 from the centre of which the air thermometer was suspended. Its 

 bulb was 4 feet above the earth. The surface thermometer was 

 placed upon a layer of cotton wool, on a spot cleared of heather, 

 which thickly covered the rest of the ground. The outlook from the 

 thermometers was free and extensive ; with the exception of the iron 

 hut just referred to, there was no house near, the hut being about 

 50 yards distant from the thermometers. 



On November 11th, at 5.45 p.m., these were placed in position, and 

 observed from time to time afterwards. Here are the results : — 



6 p.m Air 36° Fahr Wool 26" Fahr. 



8.10 „ „ 36 „ 25 



9.15 „ „ 36 „ 25 



air almost dead calm, sky clear, and stars shining. 



November 12th, the wind had veered to the east, and was rather 

 strong. The thermometers, exposed at 5 p.m., yielded the following- 

 results : — 



5.15 p.m Air 38° Wool 33° 



5.45 „ „ 38 „ 34 



