One of the many books I haven’t read to the end is Plato’s Republic. But I did get to the part where he speaks of Socrates’ image of everyday reality being nothing more than the shadows on the wall of a cave projected by the flickering fire. The role of the philosopher is to be able to see beyond the shadows to the true reality that causes them.
I like shadows. And I love projection. And as I grow older and more fogeyish I find that it is ever harder to use shadows as a tool for capturing the imagination of an audience, whether it be students in a lecture, or out in the wider world. What I’m talking about is the gradual demise of the overhead projector, a mainstay of teaching and lecturing for over half a century.
I gave a talk a few weeks ago at the Science Museum as part of one of their “Lates”, which they devoted to Chemistry, in honour of the IYC. I’d offered them my “How the Zebra got its Stripes” talk and a couple of weeks before, sent them both my risk assessment and a list of requirements – on the list was “overhead projector – dataprojector/video camera NOT suitable”.
When I got to the venue, Pete Wothers was on before me, giving an entertaining talk on where chemical names come from. But there was no OHP. When Pete’s lecture ended I started asking the staff, and they expressed surprise at the request. Eventually the disappeared off leaving me to set up. After about 15 mins a group of helpers came back empty handed. One of them said to me “But there IS an OHP – look over here”, showing me an overhead document camera. When I demurred and said it was not what I’d asked for he said “But it’s exactly the same”. I got pretty stroppy at the this point and eventually I was told that they’d found a couple but that there was “no guarantee that they would work”……
Of course it did work and the talk went off quite well – as usual, from my point of view, it could have been better, but it went down well with the audience.
But the OHP thing was annoying, and it’s not just the Science Museum.
At UCL, OHPs were withdrawn last year by our Estates Management team because they are expensive to maintain (the film is pricey and the bulbs are getting hard to get). They also find that fewer lecturers use them and so they vanished from most lecture theatres. In extremis, Francisco Diego in Physics and I won the concession that OHPs would be left in a few key lecture theatres.
And I gave a talk for Wired last year (for which, come to think of it, I never got paid – oh well) where my use of an OHP was met with gales of laughter until they saw the demo (“oh, how retro” someone sneered), and then, to my satisfaction, they went very quiet indeed when they saw the demo.
So why am I so enamoured of OHPs? It’s not just being an old dog, incapable of doing new tricks (pace, Seasick Steve). It’s because OHPs are the last link to shadow projection, the brilliant technique perfected in the Victorian period to magnify and display all manner of delicate phenomena. If you are a fan of soap bubbles you will have read Charles Vernon Boys’ classic “Soap Bubbles: Their colours and the Forces which Mould Them” (the Dover Edition is now out of print!) in which most of the demonstrations are projected onto a screen using a carbon arc and a collimator lens. [And of course there is E. J. Hartung's wonderful "Screen Projection of Scientific Experiments", a small volume I found by accident in a bookshop in Rochester (of all places) almost 20 years ago, filled with cunning systems for throwing images of microscope slides and test tubes onto a screen - get it if you can.]
Today almost no one uses those techniques – the last person I saw doing it was the wonderful Cyril Eisenberg (an intellectual descendant, if you will, of C V Boys and author of “The Science of Soap Films and Soap Bubbles“) who uses (is he still giving lectures?) a point light source to project the interference fringes in soap films, as well as the shadows cast by the films suspended in metal frames. It is spectacular in part because it is so beautiful, but also because it is so direct.With an OHP you can also do fantastic, stark, high contrast shadow projection directly, with a device that has next to no learning curve. You switch it on and you’re there. Try showing soap films to a large audience using a webcam or document camera and you’ll find it a struggle. You have to get the lighting just right, ensure you have the proper background, and even then the results will be inferior. What is more, even if you can see the film the colours are processed first by the camera and then by the computer. They just won’t be right. One of the most spectacular demos you can do is to show optical rotatory dispersion on an OHP – the colours that emerge are magical – and they just haven’t got that delicacy using a doc cam.
What is more, videocameras have a refresh rate, as does that of the projector. Fast oscillatory phenomena like the mercury beating heart suffer from weird stroboscopic phenomena that obscure what’s going on. On an OHP they look spectacular precisely because there is no intermediary.
And what of the classic sunset light scattering demo? An OHP is exquisitely set up to let you do it in a beaker or glass. What was that? You think I should use a slide projector and a fish tank……. when did you last see one of those?
Yup. I’m having a mid-life crisis, a Victor Meldrew moment, if you will. But I see little evidence that the talks, classes, and lectures we give are actually any better these days with the tens of thousands of pounds that we are spending on ever fancier projection and recording technology than the great talks that were given before Powerpoint and YouTube. Videos and animations are fine. But you know what? I want to see it live. I want to see it for real. And I want you to see it too. And with the ever-present risk that it might all go wrong. And not because of some idiotic network failure. Show me the shadows!