linear equations it follows that for any arbitrary real number $a, F_{\mu\nu}^i$ is a solution where $$F_{\mu\nu}^{(i)}=aF^{(i)}_{\mu\nu\,\rm ret}+(1-a)F^{(i)}_{\mu\nu\,\rm adv}.$$ Moreover, any superposition of the fields $F_{\mu\nu}^{(i)}, F_{\mu\nu}^{(j)}$ etc., is a solution of Maxwell’s equations that takes into account all the sources. The familiar choice based on experience is that $a$ is equal to unity. The assumption of Wheeler and Feynman, based on the action at a distance theory of electromagnetism formulated by Schwarzschild, Tetrode and Fokker[@Schwarzschild; @Tetrode; @Fokker] is that $a$ equals $1/2$, so that the physically significant solution of Maxwell’s equations is the time-symmetric field $$F_{\mu\nu}^{(i)}=\frac{1}{2}(F^{(i)}_{\mu\nu\,\rm ret}+F^{(i)}_{\mu\nu\,\rm adv}).$$ They also asserted that there is no self-action of a particle on itself: $$F_{\mu\nu}(i)=\sum_{j\not=i}F_{\mu\nu}^{(j)},$$ where $F_{\mu\nu}(i)$ denotes the total field acting on particle $i$.

Dirac[@Dirac] showed that the force of radiative reaction is relativistically deduced by means of the time-symmetric field described by $$F^{(i)}_{\mu\nu\,\rm react}=\frac{1}{2}(F^{(i)}_{\mu\nu\,\rm ret}-F^{(i)}_{\mu\nu\,\rm adv}),$$ which acts only on particle $i$. Observational classical electrodynamics is governed by the field $$\label{retarded}
F_{\mu\nu}(i)=\sum_{j\not=i}F^{(j)}_{\mu\nu\,\rm ret}
+\frac{1}{2}(F^{(i)}_{\mu\nu\,\rm ret}-F^{(i)}_{\mu\nu\,\rm adv}).$$ The time-symmetry of this equation also allows the equation to hold: $$\label{advanced}
F_{\mu\nu}(i)=\sum_{j\not=i}F^{(j)}_{\mu\nu\,\rm adv}
-\frac{1}{2}(F^{(i)}_{\mu\nu\,\rm ret}-F^{(i)}_{\mu\nu\,\rm adv}).$$

An absorber theory of radiation will act in the following way. At each point $O$ on a 