A spell that causes partial memory loss
The following evidence suggests that Gilbert Norrell was able to perform a spell that causes partial memory loss.
In January 1807 John Segundus and Mr Honeyfoot paid a visit to Hurtfew Abbey, Norrell's residence. There Norrell gave them a tour of his library, where they met Norrell's servant John Childermass and examined many of the texts in the collection .
Later that month however, when relating these exciting events to the Learned Society of York Magicians, they were unable to recall any of the contents - or even the titles - of the books which had struck them with so much admiration. They had a general recollection of having visited a wonderful library, but the details escaped them.
Furthermore, in February when Mr Segundus met Childermass for the second time he could not recall having met him before. He felt as if he knew him - that Childermas was someone he had seen already - but he could not recall where. Childermass appeared fleetingly both vexed and amused when Mr Segundus suggested they might have met:
"Something shifted in Childermass's dark face, but it was gone in a moment and whether it had been a frown or laughter it was impossible to say".
He does not remind Mr Segundus however of their former meeting in the Library, and instead contents himself with suggesting places it is likely they might have met.
This behaviour suggests it is very probable Childermass has only just deduced what has happened. After all, no-one knows better than he the obsessive jealousy Mr Norrell feels towards his precious books; nor does anyone better know what covert weapons the magician is capable of using to defend his treasure. His behaviour suggests he sees all this instantly - sees what has happened, guesses the nature of Norrell's spell and its consequences - feels both exasperation at Mr Norrell's action, and yet amusement at it. And when Mr Segundus struggles manfully to recall their previous encounter - "Oh! I shall have it in a moment!" - "Childermass raised an eyebrow as if to say he very much doubted it."
The precise nature of the spell is unknown. It might have been a permanent enchantment, part of the library's defences, similar to the one Norrell put in place to make the library nearly impossible to find: or it could have been cast by Norrell on the two visitors on that specific occasion.
Finally, we should in fairness bear in mind the possibility that the spell does not exist at all, and the strange occurrence can be explained purely by Mr Segundus's and Mr Honeyfoot's forgetfulness - though this is perhaps not so very likely. The disturbing physical effects of this episode are well-described by Mr Segundus: "I am not ill, but this last week I have felt very heavy and stupid. Mrs Pleasance has given me arrowroot and hot concoctions of liquorice root, but they have not helped - which does not surprize me for I think the confusion is in my head." (It is not clear by-the-by what Mrs Pleasance was hoping to achieve by her physic, for the effect of arrowroot is rather to bind the digestion whereas that of liquorice is the reverse: but perhaps she was merely baffled as to the cause of the malaise.).
This episode, though apparently trifling and even a little ludicrous, does however indicate quite early in our story the ruthlessness of Mr Norrell in furthering his own ends; for plainly he has here committed a kind of intimate assault upon Mr Segundus. That the victim cannot detect it nor the law punish it does not lessen the moral failure.