E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Holding the eel of science by the tail. That is, to have an ephemeral smattering of a subject, which slips from the memory as an eel would wriggle out of ones fingers if held by the tail.
Cauda tenes anguillam, in eos apte dicetur, quibus res est cum hominibus lubrica fide, perflidisque, aut qui rem fugitivam atque incertin aliquam habent, quam tueri diu non possint.Erasmus: Adagia, p. 324. (1629.)
To get used to it, as a skinned eel, i.e. as an eel is used to being skinned. It may be unpleasant at first, but habit will get the better of such annoyance.
It aint always pleasant to turn out for morning chapel, is it, Gig-lamps? But its just like the eels with their skinning: it goes against the grain at first, but you soon get used to it.Cuthbert Bede [Bradley]: Verdant Green, chap. vii.
To skin an eel by the tail is to do things the wrong way.