32 Selim Lemström. 



Fig. lo Plan I. represents the general change of température outside the 

 field of experiments, from 8 p. m. The rapid fall of température until 10 

 p. ui. is analogous Avith what usually occurs. Låter the falling becomes 

 considerahly slower, and after midnight assumes an almost constant value 

 of - 4'',o. 



If this cui've is compared with Curve IIo for the 12"" June, the general 

 changes of température will be found ahout the same. This curve is drawn 

 according to the foUowing observations: 



For Curve Iq there are observations at 8,o p. m. and at 10, is p. m. ex- 

 cept tliose made during the experiment, outside the field. 



This is, moreover, very instructive, as a cold current of air not duly 

 considered in the beginning, greatly influenced the course of the experiments. 



In the map, attention is called to the valley, which intersected the sand- 

 hill, leading to bog-lands situated farther oif. 



Through this valley a cool current af air was passing all the evening, 

 sweeping over the field of experiment C, without our being aware of it 

 that day. 



It was not untill that we discovered this circumstance and consequently, 

 on the 15"" June, a further experiment was instituted. 



If this circumstance is taken into considération, the slight difi'erence of 

 température, attained that evening, is easily accounted for. 



For the sake of a better comparison, the thermometer curve T^, for 

 point X outside the field of experiments, has been marked out on all the plans. 



The observations of the upper thermometers, represented in all the four 

 figures PI. II. 



in i-h i-n -!■,? 



