"....helping witches and wizards find their marbles since 1426."
-- Mnemosyne Clinic advertisement appearing in the Daily Prophet (DP4)
Poor Memory? is an advertisement for the Mnemosyne Clinic for Memory Modification appearing in the Daily Prophet (DP4).
“Poor memory? Forget where you left your wand? Wish you could remember spells without referring to cumbersome books?” The memory clinic says it will help – as long as you remembered to send them your contact details via Owl Post….
They promise to restore memory to “natural range” with a simple charm (DP4).
Mnemosyne comes from Greek mnēmosunē, meaning "memory". In Greek mythology, it is the name of the mother of the nine Muses (Oxford English Dictionary).
The Mnemosyne Clinic says it will can memory to its "natural range and vigour" - this assumes, of course, that the original memory capacity of the witch or wizard was any good in the first place.
Although the date printed on the fourth Daily Prophet Newsletter (DP4) is 1 October 1999, the timeframe for this event is 1992-1993.
From the Web
Writing by J K Rowling on Pottermore: The Daily Prophet
Harry Potter Wiki: Memory Charm