629 



from a lack of general co-operation, despite the fact that, for twenty years, 

 it had been used with good success by one proprietor. General co-operation 

 in any region is necessary, for otherwise a single proprietor frequently does 

 a service to his neighbor upon whose fields the wind drives the smoke, 

 without obtaining any service in return. Special regulations for the use of 

 smudges are not necessary. Any clear night, toward morning but before 

 sunrise, the fires are lighted and fed with damp litter, moss, straw, etc., in 

 which care is taken that the thickest possible smoke is carried over the fields. 

 Naturally the warmth produced by the fire is not effective here; it 

 cannot be felt even a short distance away from the centre of the flame, but 

 the smoke, like the straw mats spread by gardeners over the plants, or like 

 clouds, is beneficial since it prevents too great cooling from radiation. We 

 know from Tyndal's discoveries that a number of substances, like carbonic 

 oxid gas, carbonic acid, marsh gas, ammonia, hydrogen sulfid and volatil 

 oils, in the finest possible distribution in the air, reduced to a very small 

 amount its capacity for letting through rays of warmth. Water vapor^ 

 has a like eifect. Tyndal determined that this took up an amount of heat 

 fifteen times greater than that taken up by the whole (impure) air in which 

 it was distributed. The process is, therefore, as follows: — During the day, 

 the sun sends its heat to us in radiant and dark rays, part of which the soil 

 reflects, but absorbs the greater part, which it retains until the air becomes 

 cooler than the soil. When this condition appears an equilibrium of heat 

 tends to set in, since the earth now gives up its heat to the cool air in the 

 form of dark rays. If, however, the lower layers of the air are stronglv 

 laden with one of the above-mentioned gases, or with water vapor, the vapor 

 itself takes up the warmth radiating from the soil, instead of conducting it 

 into the upper regions of the air. Tyndal shows how great the amount of 

 heat is, which is taken up by the lower layers of air. "If we consider the 

 earth as a source of heat, at least 10 per cent, of the heat given oft" by it is 

 held within ten feet of the upper surface." By this absorption of the dark 

 rays of heat the lower layers of the air, rich in water, form a protective 

 mantel about the earth which, as a result, does not cool down so far as it 

 otherwise would. The smoke produced by the fire is, therefore, an artificial 

 covering, full of water vapor, which, in combination with the still partially 

 unknown products of distillation, decreases the permeabiHty of the atmos- 

 phere for the dark rays given out by the surface of the field. 



We omit a special enumeration of the commercial smoke candles and 

 bricks recently made for the purpose of producing smoke at the time of 

 frost, since new ones will always appear with the advance in technic ; refer- 

 ence to the existence of such articles is sufficient. It need only be mentioned 

 that, recently, in smoking vine3^ards, the smudging material was carried 

 about in carts^ in order to overcome the blowing of the column of smoke 

 by suddenly changing winds. The use of smoke carts is said to be the most 



1 Tyndal, Die Warme betrachtet als eine Art der Bewegung-. Deutsche Ausgabe 

 von Helmholtz und Wiedemann 1867. 



2 Burger, Raucherlvarren. Prakt. Ratg. im Obst- u. Gartenbau 1906, p. 128. 



