94-95] STilEAM-LINES DUE TO A SPHERE. 137 



Again, the stream -function due to two double-sources having 

 their axes oppositely directed along the axis of x t will be of the 

 form 



^ = 



T ri s 



where r ly r 2 denote the distances of any point from the positions, 

 PI and P 2 > say, of the two sources. At the stream-surface i/r = 

 we have 



