Equipotential curves on horizontal plane (Red). 
Apparent line of horizontal foree (Black). 
Fig. 4. 
1 
0 1 5 10 
L_1_1_1_4__1_I_I_J_I_J 
D represents the position of Doublet. 
P the point where its axis meets the horizontal 
plane. 
Forces in Meridian Section. 
