BRIDGMAN. — THE ELECTROSTATIC FIELD. 



625 



changing the parameters of two families of curves, while keeping their 

 shape constant, may change the shape of the family obtained by adding 

 the parameters. At distances remote from the charges, the shape of the 

 curves of Figures 1 and 2 are the same, but on approaching the rods the 

 equipotential surfaces become infinitely close together, but never cut 

 the rods. It was impossible to draw this, and the space about the rods 

 was left vacant. The lines of force were drawn in free-hand. In three 



Figure 8. 



dimensions there is no geueral additive force function corresponding to 

 that in two dimensions. 



Figure 3 represents the same combination of elements as Figure 1, 

 except that now the signs of the charges are opposite. At the point, 

 distant half a unit from the origin, through which the dotted lines pass, 

 the potential has a stationary point. The lines of force point radially at 

 this point from four perpendicular directions ; at the point itself, the 

 vol. xli. — 40 



