362 Andr. Lundager 



conspicuous with 9.1 mm. spread over eight days. Until the 10th it 

 appeared as snow, and not till the 24th as rain; but besides this 

 measured moisture another factor is utilised-in addition to the most 

 important of all which is, of course, moisture due to the melting process — 

 viz. the fog; the causal connection of this is less conspicuous but 

 certainly of no less importance both directly and indirectly. At the 

 end of the month we often had south-easterly winds and a dense fog 

 from the sea crept over the land, where it soaked everything, and this 

 sometimes happened several days running. For lichens and mosses 

 this form of moisture is undoubtedly of the greatest importance, but 

 the whole vegetation profits by direct absorption; to this should 

 be added its indirect significance to evaporation which is modified 

 to a high degree when the fog lies densely upon the surface of 

 the earth. 



Under such circumstances the temperature of the ground and the 

 water, provided currents do not supervene, is the same at night as by 

 day and coincides very nearly with that of the air. This is proved 

 by the following interesting measurements. 



After an almost constant temperature, on the 24th of June 1907 

 (-{- 3.4% + 3.7°, + 3.2° at 8 a. m., 1 p. m. and 9 p. m. respectively) I 

 measured the temperature at night at 1 a. m. in a wet moss-tuft, again 

 in a small stream and still again in a damp S//e/je-tuft and obtained 

 everywhere +3.4°; the air was then -[-2.9°. 



In the main channel of Vester Elven, where the current is rather 

 strong, the temperature, on the other hand, was only + 1.8°. The water 

 on its way from the place of melting is not under the influence of the 

 rays of the midnight sun when there is a dense cloud-covering as was 

 the case here. In the evening of the 24th, at 9 o'clock, the wind was 

 N. fast С and the cloud-covering was 10^"^ ni. ^ 



As the temperature, also, is of the greatest importance to the 

 plant-life, not only must the supply of heat be able to be relied 

 upon, but also it is necassary to economise that which has already 

 been obtained; the point is to have as slight a loss of heat as possible. 

 And here the cloud-covering also plays a great part in the condition 

 of the plant-life. 



We have above an example of the influence of the nimbus-clouds 

 directly to impart moisture, and indirectly to retain the heat b}"^ 

 moderating the evaporation. A dense covering of stratus-clouds also 

 serves the latter purpose; but they are far more favourable to the 

 vegetation when the conveyance of heat is concerned. While the 

 fog was always coincident with low temperature, there might very 

 well be conveyed to the ground a considerable amount of heat in 



' Here and everywhere the figures indicate the amount of the cloud-covering, and 

 ni., str. and fr.-str. stand for nimbus, stratus and fratus-stratus respectiveh'. 



