46 Sblim Lemsteöm. 



the surface of the earth, faintly at 3,45 a. m., but very intensely at 6,10 a. m. 

 To begin with, the falling, over-cooled mist was heated by the lower warm 

 layers of aii', hut these being gradually cooled down to zéro, it retained its 

 low température and, upon touching solid objects on the earth, turiied into ice 

 and hence occurred the l'elatively thick covering of ice \\hich was to be ob- 

 served even on the outward glass-tubes of the thermometers. That the phe- 

 nomenon did take place in this manner, is further proved by the fact that 

 highei' places, as the surrounding hills and the relatively highly situated vc- 

 randah, on the buildings of the estate, could expérience so great a fall of tem- 

 pérature, that formation of ice occurred on the former and that the température 

 of the psychrometer-thermometers on the låter wentdown to near O". Still at 3,45 

 a. m., the last-named showed a température of almost V, o, but the grass 011 the 

 ground a\ as not covered with hoar-frost, and could not be so, the thermometer on 

 the ground, in the relatively low place of observation, showing 2",3; but two 

 houi's låter the formation of ice had taken place and the thermometers in the 

 verandah had fallen to t>". Indeed, tlie objection might be made here that the 

 intensity of radiation was greater from higher places because the layer of mist 

 above them was thinner, but, on the other hand, the air cooled by radiation 

 did not stay above them, but was constantly pouring down, which undoubtedly 

 counteracted a greater intensity of radiation of heat. 



The formation of ice in higher and lower places can, therefore, not be 

 explained by radiation from the surface of the earth alone, so the cause must 

 be found in the falling. over-cooled thin mist. That the thermometer on the 

 ground, in spite of its outward tube being covered with ice, did show so high 

 a température, is finally a most evident proof that the température on the 

 ground had not fallen below zéro in conséquence of radiation, but that the 

 low température, immediately above the surface of the earth, was caused by 

 another circumstance, i. e. by the falling, over-cooled mist. 



Immediately after the observation of 3, +5 a. m. a potato-plant was marked 

 out near the place of the thermometers. Some leaves, blackened in conséquence 

 of a disease, were torn off and only the new green ones left. 



On the observation at 6,10 a. m. this plant, like the others in the field, 

 was thickly covered with ice, which, however, did no damage, for several days 

 aftei'wards the plant remained green and fresh, like the rest of the plants in 

 the field. Consequently, the thick covering of ice did not damage the plant, 

 which, on account of its sensitiveness to frost, could most probably not have 

 been the case, if the formation of ice had been caused by direct radiation. 



