The vacuum permittivity appears originally in Maxwell's equations, used to describe electric fields. The permeability of vacuum was defined using Ampere's force law (itself derived from Biot-Savart law): If two current carrying wires were spaced one meter apart, both carrying one ampere of current, the force exerted against each of the wires would be exactly $2*10^-7 N$. This also defined the ampere. Therefore, the value of vacuum permeability was fixed to $4π*10−7 H/m$ by definition.
Using his laws, Maxwell was able to produce a wave equation with the speed:
$${\displaystyle c={1 \over {\sqrt {\mu _{0}\varepsilon _{0}}}}.}$$
This turned out to be the same as the speed of light (already measured using other means), so light was deduced to be an electromagnetic wave. Here $c$ was already known, $\mu_{0}$ was defined, but how was $\epsilon_{0}$ found? Was it experimentally determined? If so, how was it found in Maxwell's times? Today, also the speed of light is defined exactly, so $\epsilon_{0}$ also now has a defined value, but clearly this was not always the case.
The reason I'm asking this is because research into this turns up a huge amount of contradicting information and circular logic, so I want to be clear on this.