LIGHTNING- — PEEK 



195 



There are no ground hits in an area between the rod and four rod 

 lengths away. This protected area is well illustrated in Figure 34 

 and seems to hold for all conditions as shown in Figure 36. 



The division of hits as the storm center moves away from the rod 

 is illustrated in (b) and (c) Figure 35. Eventually, a distance is 

 reached when the rod is no longer struck. This occurs for this 

 particular rod when the projection of the storm center is about 30 

 per cent of the cloud height away from the rod. There are no 

 ground hits closer to the rod than four times its height for the ex- 

 tremes given in Figure 35. 



DIVISION OF HITS BETWEEN ROD AND GROUND FOR DIFFERENT HEIGHTS 



OF ROD 



The division of hits between a lightning rod and ground, when the 

 rod is located directly under the storm center, is shown in Figure 



^0 02 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 Z.O 2.1 2A 

 Height of Rod in Percent of Cloud Height 



Fig. 37. — Division of hits between rod and ground for 

 different heights of rod 



37. When the rod has zero length, 100 per cent of the hits, of 

 course, must strike the ground. When the height of the rod is 1.1 

 per cent of the cloud height, the division of hits is equal, while 

 all of the strokes go to the rod when it is about 2.5 per cent of the 

 cloud height. Over this range the ground was never hit nearer to 

 the rod than four times its height. 



HITS PER UNIT AREA UNDER A STORM CLOUD 



Figure 38 shows the ground hits per unit area at various dis- 

 tances from rods of different heights. The rods are directly under 

 the storm center. With rods of zero height 1 per cent of the hits 



