Smudges for Frosts. 111 
efficient appliances for evaporating water could be 
secured for about $15 an acre for the first cost. 
“The amount of water required to raise the temper- 
ature in the space immediately surrounding a_ ten- 
acre tract would be about 500 gallons. This I have 
demonstrated by a very complete mathematical cal- 
culation based on experiments, but I have concluded 
that it would require about four or five attempts 
during a night, in order. to supply the heat radiat- 
ing into space, which would make the water re- 
quired to be spent for a ten-acre grove, about 
2,500 gallons. * * * * ‘The fuel required is 
equally certain and capable of calculation, and would 
be about one barrel of oil, costing in Los Angeles 
50 cents.” 
The making of smudges.—Frosts occur on clear 
nights. This is because the earth’s heat radiates 
quickly into space. When clouds or fogs are pres- 
ent, this radiation is checked. It is possible, in 
many cases, to supply a blanket of smoke to check 
radiation; and if this cover also contains much 
vapor of water, its efficiency will thereby be greatly 
increased. 
The use of smoke or smudges to protect plants 
from frost is an old practice. It is necessary, in 
order to secure the greatest protection, that the 
smudge be dense and uniform, and especially that 
it be maintained until all danger of frost is past. 
The best results are nearly always secured on level 
lands, where the smoke will not drain away, and 
where there are no higher lands from which the 
