60 Selim Lbmström. 



lighted simultaneously, so that they ail are burning at 11p. m., it is evident 

 that thns we hâve 5 currents of ascending warm air witli a section of abont 

 100,000 ni'"^ each. It is, of course, quite natural that the différent ascending 

 currents of air produced by the torches will ewentually join one current of 

 this section. 



These currents of air cause a disturbance in the equilibrium of the layers 

 of air, because the air pours in from all sides toward the places where the 

 torches are burning. 



The question now is, whether this disturbance is sufficiently extensive to 

 prevent a threatening frost, or, in other words, whether the air-currents, rising 

 in ail directions, are strong enough to blend the layers of ah' and thereby 

 carry to the vegetation sufflcient heat to enable it to withstand frost. 



To give an idea of the quantity of heat which is required to blend the 

 layers of air in an area of 500 hectares, with a constant température of above 

 O", we will apply the calculation, page 26. 



A layer of air of 1 m in height to 500 hectares, at an average tempera- 

 tui'e of O", will weigh 



6,465,000 kg. 



Should the upper layer of air of 1 m in height, or 2 m from the siuface of 

 the earth, be 3" warmer, its weight will be 



6,395,000 kg. 



The différence is 



70,000 kg. 



In order to keep the température above 0'^, we must according to the hy- 

 pothèses in the above-mentioned page, raise this mäss of air 



14,4 times 3 m higher 

 or use a w^ork of 



3,024,000 kg meter 

 corresponding to 



7032,5 Oal. 

 or about ^ kg of coal. 



The higher the température of the uppei' layer of air rises, the greater 

 will be the work to raise it, but the shorter will be the distance, in order to 

 give the blending the desired température. 



