linguistic:translation
Propagation of Electric and Magnetic fields

where t r {\textstyle {t_{r}}} is retarded time or the time at which the source's contribution of the field originated, r s (t) {\textstyle {r}_{s}(t)} is the position vector of the particle as function of time, r {\textstyle \mathbf {r} } is the point in space, t {\textstyle \mathbf {t} } is the time at which fields are measured and c {\textstyle c} is the speed of light. The equation subtracts the time taken for light to travel from particle to the point in space from the time of measurement to find time of origin of the fields. The uniqueness of solution for t r {\textstyle {t_{r}}} for given t {\displaystyle \mathbf {t} }, r {\displaystyle \mathbf {r} } and r s (t) {\displaystyle r_{s}(t)} is valid for charged particles moving slower than speed of light.