Great moments in biology

Over in this neck of the woods, we are rightly proud of local lad Percy Shaw (1890–1976), the inventor of the catseye, which has saved untold lives on the nation's roads.

It is said that Shaw's invention was inspired by seeing light reflected off a cat's retina at nighttime.

It turns out that Percy Shaw wasn't the first man of science to investigate reflections from cats' retinas. This from The Eye: a Natural History by Simon Ings (pp.184–5):

In 1703, [French anatomist Jean] Mery noted that a cat's eyes shine much more brightly if you hold the cat underwater…

[W]ell over a century after Mery dunked his cat, [Swedish-born naturalist, Karl Asmund] Rudolphi turned his attention to the directionality of the shining eye. He was able to show that the reflecting eye will emit light along exactly the same line as the direction of the in-going rays. No chemical or biological process is taking place—a point he demonstrated by the simple expedient of shining lights into the eyes of a decapitated cat.

That's the way to do it.

Richard Carter

A fat, bearded chap with a Charles Darwin fixation.


  1. I can see the interest and reasoning which might lead one to try this with a cat-head, but what thought-process on earth makes you decide to hold a cat under water to look at its eyes? If that isn't a recipe for breaking every bit of glass in the lab, I don't know what is.

  2. There was method in Mery's inspired madness: the aqueous humour of the eye, as its name implies, is pretty watery... A water-to-eye interface will, therefore, not diffract light anything like as much as an air-to-eye interface. So, a cat's eye underwater will appear to spread reflected light out in all sorts of directions, rather than in a narrow beam - giving the impression that the eye is brighter.

  3. I'm sure your right, although the lower refraction will spread the reflected light less, I suspect, meaning that it is brighter to a viewer along the axis (it will of course also focus the incident light onto the back of the eye less also, so I'm not sure it is as obvious as all that).

    Whatever the optics, I still maintain that attempting to hold a cat in a tank of water while you shine a light in its eye is madness incarnate.

  4. Did you know that Percy Shaw had aTV in every room of his home? They were all on constantly, but on different channels. He claimed to have never watched any of them!

  5. It's the fact that cats have nine lives that makes them an ideal candidate for cruel and unusual experiments - bring it on I say!

  6. I would be interested to learn the origins of your cat hatred. Or perhaps it is a cat phobia? That would be ... (googling) ... ailurophobia. I have a spider phobia myself, as a result of being facially explored by one as a helpless infant. But cats..who hates cats? Except for Siamese cats. Everyone hates those.

  7. Cats see themselves as the masters, where dogs take on the servant role. I wonder if Richard has a problem with his position in the pecking order.

  8. Humble, the word phobia can mean either fear or hatred. I certainly don't fear cats, but I most definitely hate them (with a passion). My mum thinks I hate cats because I am allergic to them, but she is wrong: I am allergic to quite a lot of dogs too, but I think dogs are totally fantastic (mostly).

    My hatred of cats is purely down to the fact that they are evil incarnate: untamed, pathological killing-machines that are maintained at environmentally unsustainable levels by people who think (wrongly) that they are cute, little pets. I'm fairly easygoing and tolerant when it comes to other people's foibles (c.f. my consistent support of the right of grown-ups to smoke), but I would, in all seriousness, ban cat ownership tomorrow if I could.

    Vermin, basically.

  9. Nite, yes I had heard the story about Percy Shaw's TV sets. A bit of an eccentric, by all accounts - albeit a very rich eccentric.

    Mind you, there were only three TV channels in those days, so I guess that means he only had three tellies!

Leave a comment

Your email address will not be published. Required fields are marked *