1910.] Protection of Orchards from Spring Frosts. 559 



viz. : (1) heating the air by fires, and (2) creating a thick 

 smoke, or "smudge," as it is called, to diminish nocturnal 

 radiation. 



Heating the Air by Fires. — When well managed, this is 

 stated to be very effective. It is of little use when the wind 

 is high or when the temperature falls below 20 0 F. Some skill 

 is necessary in the management of the fires, the most serious 

 mistake being to produce an intense heat by very hot fires, 

 because this creates a strong draught which carries the heat 

 directly into the upper atmosphere, where it is of no value. 

 The practicability of the method is said to depend on the 

 fact that at night there is an inversion of temperature, the 

 air being coldest near the ground and becoming gradually 

 warmer upwards. Hence the lower air may be warmed to a 

 considerable extent before an upward draught is created. 



The best results are obtained by means of numerous, 

 but small, slowly-burning and well-distributed fires of coal, 

 wood, or whatever fuel is cheapest. Crude oils have been 

 tried and make a hot fire, but have the disadvantage of 

 forming lampblack, which sticks to the leaves and fruit. 



Oil heaters are, however, extensively used in America. 

 One make is constructed with a centre-draught tube to feed 

 oil to the flames, promote combustion, and make good use 

 of the oil. It holds five quarts of oil, will burn six or seven 

 hours, and weighs if lb. There are larger sizes, but this is 

 large enough for all practical purposes.' One hundred of 

 these heaters are often used per acre, and can be made to 

 raise the temperature from 10 to 15 degrees. They range in 

 price from j^d. to is. o^d. each. 



Considerable success has been obtained with this method, 

 and in 1908 two men in Colorado saved large crops on the 

 heated portion of their orchards, the remainder producing 

 little or nothing. This was an object-lesson to growers in 

 the State, and it is stated that in 1909 there were orchard 

 heaters in every fruit district in Colorado. In one case a 

 portion of an orchard was heated in the spring of 1909 during 

 a severe frost, and a fine crop of more than 15,000 boxes of 

 apples was secured, whereas several acres not protected by 

 heaters did not produce a box of apples, though the trees 

 were winter varieties ten years old and in full bearing. In 

 another case, in New' Mexico, 30 acres of orchard were heated 



