This book is a serious bit of kit. Its hard covers measure 28.9 by 21 centimetres, and it weighs 1.62 kilograms — 324,000 times the amount of valium, we learn on page 98, that Tom Clancy needed to appear on Good Morning America (‘Sorry to wimp out, but, shit, I was scared’). The illustrations are beautiful. Very often they are simply the letters themselves (don’t worry about handwriting, there are transcripts too), but sometimes they reference the content. For instance a photograph of butterflies accompanies the biologist Rachel Carson’s letter about watching said creatures with a friend.. The butterflies were on their final migration, and Carson was dying of cancer: ‘a happy spectacle… when any living thing has come to the end of its life cycle we accept that end as natural.’

Shaun Usher started his ‘Letters of Note’ blog in 2009. The door on which he knocked wasn’t so much open as hanging off its hinges. You can see this in his vast Twitter following, the six-figure sales for his first book and the live shows at which that book’s contents were performed. Now he has produced a sequel. Dipping into it at random (you don’t read a book like this from the beginning — that would only remind you it has to end), you realise why written communication will always be important. A letter gives you time to think. As Rachel Carson herself phrases it, the thought was something ‘I can write better than say’. Then there’s the distance you gain: Dorothy Parker sends her editor a telegram instead of telephoning because ‘I can’t look you in the voice’.

Writing also aids deception. Jessica Mitford’s parents only let her leave Britain because a friend had invited her to France — it later transpired that Mitford had faked the letter, and was off to the Spanish civil war. Then again, a handwritten letter can reveal uncertainty. For some reason John Lennon feels the need, in the course of asking Eric Clapton whether he’ll join the Plastic Ono Band, to change ‘of late’ to ‘lately’.

Sign-offs are a particular fascination. The filmmaker Hollis Frampton offers the Museum of Modern Art ‘Benedictions’. Spike Milligan takes his leave of George Harrison with ‘Love, light and peace’. Che Guevara’s final words to his children (the letter was to be read only in the event of his death) are ‘A great big kiss and a hug from Papa’. Alan Turing, shortly to plead guilty to homosexual acts, is ‘Yours in distress’, while Marge Simpson’s elegant rebuke to First Lady Barbara Bush for some disparaging comments about her family ends ‘With great respect’.

Even where the sign-off is a standard one, what sits above it can vary hugely. ‘Sincerely’ follows both Samuel Goldwyn’s congratulations to Walt Disney: ‘You have made a great many pictures, Walt… But you have never made one so wonderful, so magical, so joyous, so completely the fulfilment of everything a great motion picture should be as MARY POPPINS’; and Hunter S. Thompson’s instructions on behalf of Rolling Stone magazine to Anthony Burgess: ‘You lazy cocksucker. I want that Thinkpiece on my desk by Labor Day… Your type is a dime a dozen around here, Burgess, and I’m fucked if I’m going to stand for it any longer.’

Some of the best correspondence, as with Che’s farewell, involves children. Kurt Vonnegut sets a high school class the task of writing poems, which he insists must rhyme: ‘No fair tennis without a net.’ Days after Adolf Hitler’s death Lieutenant Richard Helms spookily uses one of the dictator’s headed postcards to write to his three-year-old son: ‘The man who might have written on this card once controlled Europe… Today he is dead, his memory dispised [sic], his country in ruins… But thousands died that it might be so. The price for ridding society of bad is always high. Love, Daddy.’

Two children who wrote to adults undergo strikingly similar experiences. Nine-year-old Anthony Hollander sought advice from the Blue Peter presenters of 1973 on how to make a living person: ‘A list of what I need… model of a heart split in half… tools for stitches’. Howard Cruse (13 in 1957) asked Dr Seuss how to become a cartoonist. He grew up to do just that, while Hollander grew up to pioneer the implanting of artificially grown windpipes into humans. Both men looked back on the encouraging replies they received, and highlighted the same crucial element. As Cruse put it to Seuss: ‘You gave me a valuable gift: you took me seriously.’

If you don’t find at least something that interests you in this book you are not a proper human being. (And unless you find almost all of it gripping I can’t imagine having a conversation with you.) Even the letter that forbids further letters is brilliant. Katherine Mansfield tells her husband’s mistress to cut out the love notes: ‘Please do not make me have to write to you again. I do not like scolding people and I simply hate having to teach them manners.’