Atom and the Charge of Electricity carried by it, 515 



would call into play forces between two charged atoms placed 

 very close together, in addition to those given by the ordinary 

 laws of electrostatics ; it would make, for example, the attrac- 

 tion between a negatively charged hvdrogen atom and a 

 positively charged chlorine one less than that between a posi- 

 tive hydrogen atom and a negative chlorine one at the same 

 distance apart. For imagine, in the first case, the atoms to 

 approach a little closer together, then, besides the diminution 

 in the potential energy due to the ordinary electric forces 

 between the atoms, there will be an increase in the potential 

 energy from the increase in the effect on the gyrostats due to 

 the rotation in the Faraday tubes ; while in the second case, 

 when the hydrogen is positive and the chlorine negative, this 

 increase will not take place. Thus the diminution in the 

 potential energy due to a given diminution in the distance 

 between the atoms is less in the first case than in the second, 

 and consequently the attraction between them is smaller in 

 the first case than in the second. If we could reach a place 

 where, as the distance between ths atoms diminished, the in- 

 crease in the potential energy due to the effect of the gyrostats 

 was numerically greater than the diminution in the potential 

 energy due to the electrostatic attraction, then the oppositely- 

 charged atoms would repel instead of attracting each other. 



Hydrodynainical Illustration. 



The following illustration also indicates that the force 

 between two electric charges may be modified by the electro- 

 chemical properties of the atoms carrying the charges. 



In a cylindrical column of rotating fluid the pressure increases 

 with the distance from the axis of rotation, so that the average 

 pressure over a cross section of the cylinder is less than the 

 pressure at the surface of the cylinder. When a solid is 

 immersed in a liquid where the pressure is uniform, the pres- 

 sures of the liquid on the solid form a system of forces in 

 equilibrium. Now suppose that a column of the liquid abut- 

 ting on the solid acquires rotation, the pressure on the part of 

 the solid in contact with the column will be less than the 

 pressure outside, the pressures on the solid will no longer be 

 in equilibrium. The defect in pressure over the cross section 

 of the column will give rise to a tension acting on the solid. 

 This tension is equal to the excess of the pressure over the 

 cross section, when the pressure is uniform and equal to that 

 at the surface of the cylinder, over that actually exerted over 

 the area by the rotating liquid. If the rotating column is a 

 cylinder containing a number of vortex filaments mixed up 



