On Night-Frosfs. 57 



We hâve, therefore, tlie followiiigtable: 



For 10 hectares 1,100 torches 



„ 5 „ 600 to 650 



„ 4 „ 500 to 550 



„ 3 „ 400 to 450 



„ 2 „ 270 to 320 



„ 1 „ 160 to 210 



„ 0,5 „ 100 to 150 



As the nuinber of torches to be held in l'eserve for special currents of 

 cokl air cannot be deterinined exactly, the whole nuinber necessary cannot be 

 accurately tixed. The smaller the area to be protected, the larger the iiuni- 

 ber of torches must be, in proportion to its size, for a current of cold air from 

 the surroundings may always be expected. 



If the tield in question is snrrounded by forest or hills so that no opeu 

 fields lie between, the number of torches can be diminished by 10 % to 20 % 

 and this may also be doue when the tield lies on a slope and is well diained 

 wiht open ditches. 



Deep and sloping ditches are first filled with coldair and then carry it 

 way in large (juantities and thus the height of the layer of air gi'ows much 

 more slowly on a tield with shallow ditches and gentle sloping. 



As we hâve pointed ont before, the torches are now so consti'ucted that 

 the principal part of the burning mateiial, or the tubes of tui'f, when thoroughly 

 dry, can be laid ont beforehand in the field which is to be protected. Tliey 

 eau remain there in ail weathers, while there is any fear of frost, or until 

 they are used. If not required, tliey can be gathered up and put away. If 

 there is danger of frost on any night and they are to burn, two men must 

 procced to the field, one carrying a basket of well-dried kindling-cylinders and 

 a small measure of petroleum (2 — 3 liters), the other a lighted torch. One 

 moistens the kindling-cylinder by dipping one edge of it in the petroleum, and 

 then sliping it into the tube of turf, which must be placed on the ground in a 

 sloping position. The other ignites the kindling-cylinder, which at flrst burns 

 in a rtame for some miiuites, and then begins to glow, setting the turf-tube on 

 fire by its heat. In an hour, or a little more, the turf-tubes are one glowing 

 mass, spreading heat and aq. vapour in ail directions, though less than at first. 

 As, in this method, wai'm moistui'e lias prédominant influence, it is advisable 

 to increase its production b}' heaping damp moss, if such is to be liad, or even 



