On yh/hf-Fro.-ifs. 7 



The gaseous matter round the earth hinders tlie radiation of heat in so 

 inuch as it retiirns the heat to the earth nioi'e or less and tlms compensâtes 

 for the loss. 



ïhe intensity of the fall of température caused hy the radiation dépends 

 on the following circumstances : 



l:o. The aqueous vapour of the air and différent elements in it. 



The heat which radiâtes to spare arises in most cases from plants on the 

 surface of the earth. The plants receive heat from helow hy radiation from 

 the hare earth and hy conduct through the plants themselves and give ont heat 

 first to the atmosphère, and on its state dépends the intensity of the fall of 

 température. 



From the latest researches on the powers of emission and ahsorption of 

 gases it springs clearly that: 



the pure and clear air is nearly diatherman for the heat 



the carbonic acid, even in small quantifies with which it is contained in 

 the atmosphère, exercises a perceptible absorption which yet is not determined 

 with sufticient exactitude. 



Concerning otlier small gaseous matters in the air, thej' probably hâve 

 very little influence, which also seems to be the case with the nitric oxides 

 and the ammonia, though being the most absoi'bing ones. 



Aqueous vapour and ivater. Though the controversy on the ahsorbing 

 power of vapour of water is not yet fuUy decided, there are however so 

 many experiments favouring the opinion, that this power on the dark rays of 

 heat is hardly greater than that of air. Concerning the power of liquid 

 water, that is to say in this case, Condensed vapour, ail agrée that it is great 

 and attains nearly 90 per cent of radiated heat. 



Though dust or the solid particles of différent kinds in the air exists 

 only to a small extent, its influence is still very great. Acknowledging the 

 fact that clear air and transparent vapoui' do not radiate or absorb in a marked 

 degree, the principal radiation from the atmosphère itself falls in the very 

 beginning on thèse solid particles and their rôle becomes that of leading into 

 condensation of vapour, being first cooled down under the température of the 

 surroundings and then attaining the de"\v-point. The condensation once begun, 

 the radiation hästens towards the earth as well as to space, because the 

 radiantpower of the atmosphère is increased by the Condensed vapour and it 

 is soon formed into a cloudy veil. 



