376 AM)It. Li NDAdKIl 



The dilTerence between insolation and non-insolalion was practi- 

 cally nil. Jiisl at midday, Ihe clTect was soniewhal noticeable it" 

 the llu'iinonieltr, as in this case, was placed high up, where it could 

 catch the rays of the low-lying sun -surreptiously as it were. On 

 level ground the elTect was almost unnoliceable. 



When no mention is made of the amount of cloud, the observations 

 have been made beneath a cloudless sky. The amount of cloud 10 

 with the exponent signifies that the sky was entirely covered with 

 a thin layer of cloud. 



The observations of the insolation which especially concern the 

 midday radiation dilTer most astonishingly from the temperature of 

 the air, so long as this is still low — therefore, early in the year, 

 although the sun's altitude is then also low. A comparison of two 

 measurements shows that the difference was less on July 31 than 

 on March 31 1907, and that the rise in the temperature of the 

 insolation does not keep pace with the rise in the temperature of 

 the air, in spite of the sum-total of the radiation lying naturally 

 nearer its maximum in July than in March. 



Air xu ^ 1. Difference 



triermometer 



March 31, at 11.30 a.m. —19.5 +18.0 37.5 



July 31, at 1.0 p.m. + 1 0.3 -f 42.0 31.7 



Difference 29.8 Difference 24.0 



The sun's altitude, respectively: 17^14' and 31°36'. The sun's 

 culmination at Danmarks Havn 36°4r. 



Notwithstanding the problematic value of these figures to indicate 

 the warmth which is conveyed to the vegetation by the radiation, 

 I have employed them, well knowing that they do not afford absolute 

 data for arriving at a decision. We have no means of establishing 

 such data, as we do not possess any registration-apparatus which 

 can indicate the course of the radiation through any complete period 

 — twenty-four hours a week, or longer — which would perhaps 

 illustrate the conditions rather more reliably, and especially might 

 be able to give us a better idea of the sum-total of the radiation. 



We know from experience that there is a supply of warmth, 

 but its magnitude depends on many factors; the conditions of the 

 country and the nature of the ground play their part, as the height 

 of the sun in the sky at different times also plays its part. 



In addition to the measurements which have already been given 

 of the temperature at the surface of the ground, amongst plants, 

 and in pools, lakes and rivers, with special reference to its relation 



