38. Expression of the properties of the Electric Field in terms of Faraday Tubes. The results we have hitherto obtained only depend upon the fact that two charged bodies are attracted towards or repelled from each other with a force varying inversely as the square of the distance between them; we have made no assumption as to how this force is produced, whether, for example, it is due to the action at a distance of the charged bodies upon each other or to some action taking place in the medium between the bodies.

Great advances have been made in our knowledge of electricity through the introduction by Faraday of the view that electrical effects are due to the medium between the charged bodies being in a special state, and do not arise from any action at a distance exerted by one charged body on another.

We shall now proceed to consider Faraday's method of regarding the electric field–a method which enables us to form a vivid mental picture of the processes going on in such a field, and to connect together with great ease many of the most important theorems in Electrostatics.

We have seen in Art. 15 that a line of force is a curve such that its tangent at any point is in the direction of the electric intensity at that point.