Thanks go to Tess Kincaid who hosts this writing meme.

To: Messrs Lea and Gibbs
Sirs,
I am indebted to you for your correspondence of 9- M- 1840 and
am honoured to be the recipient of the first adhesive postage stamp in the
world (or one thereof)
I beg to suggest that the stamp hereafter referred to as the
‘Penny Black’ should be conserved with care. It is unfortunate that some have
already been ‘cancelled’ though I understand the red ink used in the
cancellation may be easily removed, allowing them to be re-used, thus
permitting some economising.
As an amateur philatelist I would be interested to know if
there are any sheets of six or more available.
I remain, Sirs, Your Servant,
Daniel
Cooper
There follows his (supposed)
correspondence with a young lady.
My Dear,
I am currently engaged in communication
with Messrs Lea and Gibbs with a view to acquiring a sheet of ‘Penny Blacks’ which
I surmise may be of considerable value in years to come.
Philately is an interesting
pursuit and I am convinced it could become lucrative.
I remain, etc, etc
From Wikipedia: The Penny Black is not a rare stamp. The
total print run was 286,700 sheets with 68,808,000 stamps and a
substantial number of these have survived, largely because envelopes were not
normally used: letters in the form of letter sheets were folded and sealed, with
the stamp and the address on the
obverse.
If the letter was kept, the stamp survived. However,
the only known complete sheets of the Penny Black are owned by the British
Postal Museum. Though not rare a Penny Black in mint condition
might fetch £3 – 4,000.
From Wikipedia: Cooper
was a founder and the first president (1869–78) of the Philatelic Society of
London, the predecessor of today's Royal Philatelic Society London. His Australian postage stamps, sold to Judge Frederick Philbrick in 1878 for £3000 (the first four-figure
price for a collection), became part of Ferrary's celebrated collection. The Sir
Daniel Cooper Lectures, sponsored by the Royal Philatelic Society, are in his
honour.