518 Prof. J. J. Thomson on the Relation betiveen the 



the same direction as the fluid in the tube, we may regard the 

 action between the gyrostats and the tube as equivalent to a 

 couple tending to increase the moment of momentum of the 

 fluid in the tube, and thus to increase the pull exerted by the 

 tube on the atom. When, however, the rotation of the gyro- 

 stats is in the opposite direction to that of the fluid in the 

 tube, the action between the atom and the tube will be equi- 

 valent to a couple tending to diminish the moment of 

 momentum of the fluid in the tube, and thus to diminish the 

 pull exerted by the tube on the atom. Thus if, as before, 

 we suppose that the gyrostats in the hydrogen atom are 

 rotating in the same direction as the fluid in the Faraday 

 tube of which it is the origin when it carries a positive charge, 

 whereas the gyrostats in the chlorine atom are rotating in the 

 same direction as the fluid in the Faraday tube of which it is 

 the termination when it carries a negative charge, we see 

 that the attraction between a positively charged hydrogen 

 atom and a negatively charged chlorine one will be greater 

 than that between a negative hydrogen and a positive chlorine 

 atom separated by the same distance. 



The object of these illustrations is to call attention to the 

 point that when charged atoms are close together, there may 

 be forces partly electrical, partly chemical, in their origin in 

 addition to those expressed by the ordinary laws of electro- 

 statics. 



There are one or two points in connexion with the theory 

 of the electric field which can be illustrated by the conception 

 of a Faraday tube as a bundle of vortex filaments, which, 

 though not connected with the main object of this paper, may 

 be briefly pointed out. The first of these arises from equation 

 (4), p. 516, which indicates that the tension exerted by a 

 vortex column is equal to the kinetic energy of the fluid 

 in unit length of the column. Now we know that the 

 forces on a charged body in the electric held are such as 

 would be produced if there were a tension along the lines of 

 force equal per unit area to the electrostatic energy in unit 

 volume of the field. If we suppose the tension to be exerted 

 by the Faraday tubes and the energy to reside in these tubes, 

 this is equivalent to saying that the tension exerted by each 

 of these tubes is equal to the energy in unit length of the 

 tube. This exactly coincides with the result indicated by 

 equation (4), if we suppose that the Faraday tubes are bundles 

 of vortex filaments. 



The other point is in connexion with the view that mag- 

 netic force is due to the movement of the Faraday tubes : the 

 magnetic force being at right angles to the direction of the 



