The Nature of Physical Theory: A Study in Theory of Knowledge

By Victor F. Lenzen | Go to book overview

CHAPTER VI
ELECTRODYNAMICS

1. ELECTROSTATICS

WE shall build the theory of electricity and magnetism upon the definition of force given in dynamics.

As early as the time of Thales it was known that if a rod of amber is rubbed it will attract light bodies, such as small bits of paper. Bodies consisting of other substances also possess this property; if one rubs the hard rubber barrel of a fountain pen on a piece of cloth it will attract light bodies. Bodies which exhibit these properties are said to be electrified, or to have the property of electrification. Thus we ascribe electrification to a body when it is the condition of an acceleration, in some other body, which is not directly describable in terms of gravitation, mechanical pressure, etc. We say that an electrified body is the origin of a field of force which is ascribed to the vicinity of the body in virtue of the accelerations experienced by bodies in the field. Speaking uncritically, we may say that the property of electrification is defined in terms of the effects of electric action. Electrification is not a property which is immediately apprehended like color, sound, hotness, etc.; the state of electrification is attributed to bodies in order to describe observable interactions with other bodies.

Simple experiments reveal that electrified bodies exert forces on each other which are either forces of attraction or repulsion. From experience we obtain laws of the attraction and repulsion of electrified bodies, and then transform these laws into postulates which implicitly define the concepts of similarly electrified and dissimilarly electrified bodies. By definition two bodies are similarly electrified if they repel each other; dissimilarly electrified, if they attract each other. It is obvious that these concepts are applicable to experience: an electrified glass rod is said to be positively electrified; a body

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