120 The Principles of Fruit-growing. 
fan. A windmill may sometimes be set in motion 
by water-power or other means. 
Heating the air.—It is sometimes possible to di- 
rectly heat the air by means of large fires, although 
such practice does not seem to have generally met 
with encouraging results. In the combined smoke 
and vapor smudges which have been commended by 
Hammon (page 112), the heat of the fire may add 
something to the efficiency of the protection. The 
strong currents of air which are set up by heavy 
fires seldom aid in the protection of the plantation. 
Yet there are cases in which hot fires have saved 
trees over considerable areas from heavy frosts and 
even from freezes. One of the best experiences in 
this direction is reported from Florida by Davies.* 
In the freeze of February, 1895, he was able to 
raise the temperature in his grove from 18 degrees 
to 383 degrees by means of fires. “On the north 
and west sides of your grove have what are called 
conflagrations, big fires, that will send billows of 
heat rolling between and over your tree tops; and 
all through your groves, at short distances, have 
small fires to help on the good result.” Mr. Davies 
recommends that orange growers “get ready, and keep 
ready all the time, for the freeze. Once it has come, 
there will be no time for gathering materials for fire. 
Your fuel must be on hand, and plenty of it.” It 
is then necessary to keep the fires burning vigor- 
ously until the cold spell has passed. H. R. Ste- 
*D. O. Davies, “Protecting Orange Groves from Cold,” Fla. State Hort. 
Soc. 1896, 28. 
