Fields of Force - A Course of Lectures in Mathematical Physics Delivered December 1 to 23, 1905 #248643

And yet if we ask, what is an electric or a magnetic field of force no one will be able to give a satisfactory answer. We have theories relating to these fields, but we have no idea whatever of what they are intrinsically, nor even the slightest idea of the path to follow in order to discover their true nature. Above all other problems which are related to fields of force, and which occupy investigators daily, we have therefore the problem of fields of force, viz., the problem Of their true nature. My lectures will not give the solution of this problem, but I should be happy if they should contribute to a broadening of our view of it.