PHYSICAI, CONTROLS OF FIRES 921 



Tabi<e 3. — Relative Seasonal Importance of Fires on Different Aspects. 



Month 



South 



I 

 East West 



I 

 Level '. Total 



Per cent 



of total 



fires 



May 



June 



July 



August 



September 



October 



November 



Per cent of total 

 fires 



A study of one of the charts made shows what of course everybody 

 knows, that in the early and late part of the fire season a very high 

 percentage of the fires are on the warmer south slopes, and that dur- 

 ing the peak of the season the north and south slopes are more 

 nearly equal than at any other time. 



Another expression of this same relationship is given on another 

 chart. There are, in the data used, twelve forests for six years, or a 

 total of seventy-two points for each month. If, for example, on every 

 forest and every year fires occurred on the south slopes in August, 

 regardless of the actual number of fires, the value would be 100 per 

 cent of the possible. Likewise, if only twenty-four points were rep- 

 resented the relative value would be 24 divided by 72 or 3 per cent. 

 The values used on this chart are obtained in this way : It is seen that, 

 beginning with May, fires occur over twice as often on south slopes 

 as on north slopes, that through June and July the two approach more 

 and more closely, and that in August they are practically the same; 

 then, during September, October, and November the lines again 

 diverge quite sharply, showing that more and more the fires tend to 

 occur on south slopes. On the average fires occur only 80 per cent as 

 many times on north slopes as they do on south. 



A still further and very striking difference between north and south 

 slopes is found in the total number of fires which have occurred dur- 

 ing the six-year period. On the north slopes a total of 1.369 fires 

 have been reported and on the south slopes 2.227 fires, or about 62 

 per cent more. It may be that there is a difference of 10 or 15 per 

 cent in the area of land on north and south slopes in the National 



