42 BULLETIN NO. 161 



After examining the case where the frost takes part of the 

 crop each year let us test the case where the frost takes the 

 entire crop every few years. Let us assume that the frost takes 

 the crop one year out of every three when no heating is done. 

 The orchard heating equipment depreciates at about the same 

 rate whether it is being used or not, so that the interest and 

 depreciation during the life of the equipment must be charged 

 up to heating during the years when heating is done. There- 

 fore, if heating is done every third year, three years' interest 

 and depreciation will have to be charged up to that year. The 

 equation If or the man who heats then is : 



b( s k) c n(gr+L) 3Dh IP=iP (8) 

 and for the man who does not heat the equation is : 



0(s k) c IP=i,P (9) 



This year the man without a crop has to care for the orchard 

 exactly as if he had a crop so that c=c and P=P, and 1=1, but 

 i>ii. Subtracting (9) from (8) we obtain: 



b (s k) o (gr+L) 3Dh=P (i ij 



In order to make it pay to heat, i must be larger than i 19 which 

 makes the right side of the equation positive and the left side 

 will be positive when 



b (s k) >n (gr+L) +3Dh 



It is to be observed that this equation is just the same as the 

 one developed for the case where part of the crop is destroyed 

 each year except that the interest and depreciation for the years 

 when there is no frost is all charged up against the years when 

 there is frost so that the yield of fruit saved must more than 

 pay 'for the entire heating cost. The farmer cannot tell ahead 

 of time whether he is going to have frost that year; hence, he 

 will put his heaters in the orchard and fill them and put them 

 up again every year whether there is frost that year or not, and 

 the man who loses his entire crop through not heating will have 

 to take care of the orchard just the same as the man who has a 

 crop on the trees unless it be in the single exception of the 

 spraying so that as far as the economics is concerned this case 

 is just the same as the one just considered. Here b is the entire 

 crop and equals Ab of the other equation. 



In the above financial consideration of orchard heating 1 we 

 have assumed that heating never failed to save the crop. How- 

 ever, to have this true the orchard must be protected from 

 winds and the plan of procedure must be worked out to a nicety 

 before the time comes to heat so that there will be no accidents 



