In these lectures we are keeping off the profound and vexed question as to what we mean by 'reality.' I am maintaining the humbler thesis that nature is a system.

But I suppose that in this case the less follows from the greater, and that I may claim the support of these philosophers.

The same doctrine is essentially interwoven in all modern physical speculation.

As long ago as 1847 Faraday in a paper in the _Philosophical Magazine_ remarked that his theory of tubes of force implies that in a sense an electric charge is everywhere.

The modification of the electromagnetic field at every point of space at each instant owing to the past history of each electron is another way of stating the same fact.