the question

The study of electricity to-day comprehends a vast range of phenomena, in all of which we are brought back ultimately to the fundamental conceptions of electric charge and of electric and magnetic fields. These conceptions are at present ultimates, not explained in terms of others. In the past there have been various attempts to explain them in terms of electric fluids and aethers having the properties of material bodies known to us by the study of mechanics. To-day, however, we find that the phenomena of electricity cannot be so explained, and the tendency is to explain all other phenomena in terms of electricity, taken as a fundamental thing. The question, "What is electricity?" is therefore essentially unanswerable, if by it is sought an explanation of the nature of electricity in terms of material bodies.

-- Professor Harold A. Wilson, writing on "Electricity" Encyclopaedia Britannica (1947)

This is reminiscent of Lao-tzu beginning, "The Tao which can be explained is not the eternal Tao," and then going on to write a whole book about it; for the article which follows this paragraph is a vastly learned discussion of the properties and behavior of this unknown "ultimate."

-- Alan Watts Tao: The Watercourse Way (in which Wilson's passage is quoted)