34 Selim Lemström. 



Accordingly, the torches liad been of evident effect, in spite of tlie cold 

 current ot air. On an average, the snrplus of temperatnre proved to be 1°,9, 

 and, taking the lower température near the trench into considération ( — 4,5) 

 this surplus amounted to 2°,4; but the experiment afforded, an important lesson 

 for the future, i. e. tliat wherever a cold air-cnrrent is to be apprehended, it 

 must be stopped by putting down a larger number of torches across it. 



This would, of course, have considerably increased the effect of the torches 

 and is clearly seen from the experiment made on June IS"". About midniglit 

 hoar-frost appeared in the surrounding lield, but not till 1 a. m. in that of 

 experiments. 



Toward the end of the experiment, the thermometers at points h, c, d 

 showed a rise of température and most probably also at point a. The average 

 rise was about half a degi"ee till 2 a. m. — The day had been tolerably 

 warni, calm and clear. The surrounding flelds were not damaged. 



EXPERIMENT II. 



June 12"' 1880. 



The preceding experiment, which in some respects, had character a 

 preparatory, had been carried on a pièce of ground overgrown with short 

 grass. The second was made in tield of rye A, 2,5 hectares of which were 

 measured ont. Along the borders of the ditches, at a distance of about 6 m. 

 fi'om eacli other, 500 torches were placed regularly about the wliole field, as 

 liere no cold current of air was to be expected, like that of the first experi- 

 ment. The field was divided into plots of ground about 8 ni. in bi-eadth. On 

 the map, this field is marked ont by two parallel lines mm and nn , running 

 between the boundary of the field and the trench. — The ryefield, in which 

 this experiment took place, had small open spots here and there, caused by 

 the effect ot the spring-ice. It is evident that those motions of the air, which 

 are caused by radiation ot heat must, in a ryefield vvhere the straw is 

 över one meter in length, take place in a way considerably différent from 

 what it will be in a field covered with short grass. The first occurrence will 

 be that the ears of rye are cooled down and impart their low température to 

 the air, which sinks tovvards the ground, giving place to wai'mer air which, 

 in its turn, is cooled and sinks down. This motion goes on all night, It is 

 clear that the rye will be the better protected against night-frost, the taller 

 the straw is, for no freezing can take place before the cooled layer of air 



