Figure 27-13. Contour map of the function 



X 2 + Z 2 



/ = .002 and is in the direction of the earth's magnetic field at a point on the 

 earth's surface where the inclination of the earth's field with the horizontal is 

 60 degrees. Let it be required to compute the value of H e arising from the 

 cylinder at a point on the surface of the ground 50 meters north of the vertical 

 projection of the axis on the surface. 



If the unit of the contour map be set equal to 100 meters, then the center 

 of the circular outline of the cylinder will fall 21/9 units below the x axis and \/ 2 

 unit to the left of the z axis. To find the contribution to H z of the terms 

 containing In, we use the tenth unit divisions on the cross-section paper on 

 which the contour map is drawn to divide the circular area into vertical rect- 



angles. Values of 

 604 



X 2 + z z 



at the ends of each rectangle are then read off the 



