ON THIS WIKI
Lightning Impact is an enchantment to Ethereal Familiar, which will increase damage and knockback enemies. In order to upgrade the Familiar with a certain level, it has to be already upgraded with the previous level of enchantment.
Thaumcraft 4 Research Notes
A shocking experience
"A Familiar with this upgrade will have a sugnificantly more powerful arc when attacking, dealing more damage and a reasonable amount of knockback.
Consumes 0.03 Aer and 0.02 Perditio Vis per attack and level."Aspect the Ethereal Essence is related to has to match the Aspect the Ethereal Familiar is related to and the 4th aspect in the recipe. In this article it is
Lightning Impact I
Lightning Impact II
Lightning Impact III