Historical parallels are never exact. Each development in science is something new and different from any which preceded it. Still it may be illuminating to discuss the progress that has recently been made in quantum electrodynamics, using the historical development of classical electrodynamics as a standard of comparison. So may we see our present knowledge and our present difficulties in their proper perspective. If Faraday's appeal quoted above had been more effectively answered in his day, might not electromagnetic waves have been discovered less than thirty years later? We cannot answer such a hypothetical question. But every theoretical physicist who reads Faraday's words will be uncomfortably aware that similar appeals are still being made and are still not being answered. This article attempts to express in simple words the results of our recent thinking in quantum electrodynamics, not fully, but clearly and definitely so far as that is possible.
“There is one thing I would be glad to ask you. When a mathematician engaged in investigating physical actions and results has arrived at his conclusions, may they not be expressed in common language as fully, clearly, and definitely as in mathematical formulae? If so, would it not be a great boon to such as I to express them so?—translating them out of their hieroglyphics, that we might also work upon them by experiment.”