It is a source of continuing regret to me that I never got to send any of the fan letters I began writing to the late Stephen Jay Gould. They weren't good enough, and I didn't want to waste his time.
One of my unsent letters was on a subject which Gould said was in his top-three for reader feedback. In his essay Left Snails and Right Minds (published in his book Dinosaur in a Haystack), Gould wondered why old engravings of snails often show their shells spiralling the wrong way (the vast majority of snail shells have right-handed spirals; the old engravings often showed them left-handed). Some years after first reading the essay, I came across the following letter in Volume 5 of The Correspondence of Charles Darwin, which caused me to start drafting another unsent letter to Gould:
Charles Darwin to James de Carle Sowerby, 21st January, 1851
My dear Sir
I am much pleased with the Plates.— […] Only one figure will require a weighty alteration, viz P. rigidus. Nevertheless, I hope that you will loook [sic] over your Figures carefully for I saw a good many little blemishes; & the Plate is not very clean.—
The few reversed figures are unfortunate.— […]
Sowerby was artist to the Palaeontographical Society and was preparing the engravings for one of Darwin's barnacle books, Fossil Cirripedia (1851). From earlier letters, it is quite clear that Darwin was extremely frustrated with Sowerby's slow progress. In contrast, a few reversed figures seemed relatively unimportant—although I thought Gould would have been amused that his great hero also suffered from reversed engravings.
By a strange co-incidence, shortly after reading Gould's essay, I read a chapter in Richard Dawkins's (then) latest book, Climbing Mount Improbable, which also dealt with shells. In it, Dawkins explained how the shapes of all shells can be recreated on a computer using just three parameters (or 'genes'), which he named flare, verm, and spire. This time, I actually did write to the author:
Richard Carter to Richard Dawkins, 8th August, 1996
Dear Prof. Dawkins,
I greatly enjoyed reading your recent, excellent book, Climbing Mount Improbable and, in particular, the chapter on shells. However, I think I may have spotted a small mistake: on page 153, when talking about what you have called the spire parameter, you state:
Spire has no limits: negative values trivially indicate an upside down shell.
Although it is hard to visualise, I reckon that, if you turned this "upside down" shell the right way up, it would actually be spiralling in the opposite direction to a shell with a positive spire (anti-clockwise, as opposed to clockwise). Although this is hardly earth-shattering, I would argue that it is not trivial - after all, your favourite sparring partner, Stephen Jay Gould, dedicated an entire chapter to anti-clockwise snail shells in his recent, equally excellent, Dinosaur in a Haystack. […]
To my great delight (and my dad's: he has boasted about it ever since), Dawkins emailed me straight back, confirming the error:
Richard Dawkins to Richard Carter, 15th August, 1996
Dear Mr Carter
Thank you for your letter of 8th August.
Yes, you are correct that the computer shell with a negative spire would beanticlockwise, and it is certainly not trivial. If I had thought of this,it would have saved me the trouble of building in a separate gene for handedness. Damn! […]
With best wishes
(Let it not be said that Richard Dawkins never admitted to making a mistake.)
Then, yesterday, I spotted another interesting example of reversed images, which, bearing in mind the subject matter, I'm sure would also have amused Gould. While re-reading my recent post The Expression of Emotions in Darwin, I suddenly realised that the photograph of Darwin that was the subject of the piece also appears on the covers of two books I have recently read—but in mirror image:
A quick check of the buttons on Darwin's waistcoat on a higher resolution version of the image confirmed that the photograph of Darwin on the left is shown the correct way round, whereas the photographs appearing on the covers of the two books are shown in mirror image.
Plus ça change, as we say in Yorkshire.