Figure 221 — Similar to Figure 220, but the line of dipoles and the solid of revolution 



extend to infinity. A few streamlines outside the solid are shown by broken curves. 



See Section 133. (Copied from Reference 7.) 



An attempt to produce forms resembling actual airship hulls more closely was made by 

 Lotz, using a nonuniform distribution of dipoles on the axis, but point sources spread over 

 the surface were found to work better. (See Reference 7, page 69.) 



134. POINT SOURCE NEAR A SPHERE 



Problems involving given boundary conditions can often be solved by superposing 

 solutions satisfying the given conditions. Sometimes the process of superposition involves 

 an integration. 



The field of a point source, for example, is easily obtained by integrating that of a 

 dipole. This corresponds to the fact that physical dipoles, each consisting of a source and 

 equal sink close together, can be laid out in a row so that each source is canceled by a 

 superposed sink, except at the ends of the row. 



335 



