CHARLES AUGUSTIN COULOMB 157 



and proved the possibility of obtaining by means of influence 

 any required intensification of an existing charge, as happens 

 in the 'influence machine' to-day. 



Nevertheless, the idea of the action of the two electricities 

 upon one another, and upon like charges, was still very in- 

 definite, as was also the part played by the matter composing 

 the charged or uncharged bodies in regard to the eflFect pro- 

 duced, particularly if it could be shown that only one kind 

 of electricity (positive) exists, the other (negative) being only 

 a deficiency of the former, a possibility which could not be 

 rejected. People spoke of an 'electric atmosphere' which 

 every charged body spreads around itself, or of a 'sphere of 

 electrical action.' As compared with this, a great simplifica- 

 tion, and translation from the undetermined to the entirely 

 determined, occurred when Coulomb was able to announce 

 his laws after this state of uncertainty had existed for about 

 twenty years. For these laws actually proved sufficient to 

 render possible a quantitative grasp of all phenomena of 

 stationary electricity (electrostatics), that is of electricity 

 which had reached equilibrium after flowing along con- 

 ductors. Even Faraday's discovery fifty years later of a true 

 and essential influence exerted by the insulators surrounding 

 the conductors, only required the addition of a material con- 

 stant (the dielectric constant) to Coulomb's law, without any 

 change in the form of the latter. Coulomb had himself also 

 investigated very extensively a series of phenomena of sta- 

 tionary electricity, including the distribution of electricity 

 on conductors of different shape (particularly rows of spheres 

 and cylinders), whereby he made use of a 'proof plane' for 

 the first time, along with the torsion balance as a measuring 

 instrument; the proof plane being used to lift off, as it were, 

 the electricity situated at a certain point, on a conductor, 

 and enabling it to be measured. Above all, Coulomb con- 

 firmed by very refined methods the fact already noticed by 

 Gray, that electricity is only situated on the external surface 



