ELECTRIC DISTRIBUTION AND CONDENSATION. 67 



those farther out rush in to take their place ; creating 

 air currents around the conductor, by which its elec- 

 tricity is gradually dissipated. The removal of electric- 

 ity by the air in this way is called convection. 



VARIATION OF CHARGE. Since the insulating power 

 of the air varies greatly with its humidity and tempera- 

 ture, and since its electric potential is also variable, the 

 charge which may be condensed on a conductor will 

 vary in like proportion ; dry, cold air being much more 

 favorable to the condensation of a high charge than 

 damp, warm air; and air at a high electric potential 

 than air at a low potential. 



Analogous to this is the influence of atmospheric 

 pressure on steam ; the temperature varying with the 

 pressure under which it is generated. Here pressure 

 constitutes resistance, while in the case under consider- 

 ation the resistance is due to the causes mentioned. 



Equal electric condensation on every part of the sur- 

 face is never practically true ; as the induction of sur- 

 roundings varies, and form, as will be shown hereafter, 

 has an important influence. It could only be true of 

 an insulated sphere, surrounded by a homogeneous 

 medium, and removed from all other influences. 



INFLUENCE OF FORM. It has already been stated 

 that form exercises an important influence on the 

 amount of static charge which may be condensed on a 

 conductor ; and that a charge on an insulated sphere 

 is equally distributed over its surface, when the sur- 

 rounding induction is equal : also that the air, by its 

 insulation, retains this charge on the surface, and 

 by its convection gradually removes it. It is evident 

 also that these forces act at equal distances from the 

 center. 



