In May 1884, a group of schoolboys on a beach in Zanzibar came upon a large mass of pumice stone that had washed up at the tidemark. Evidently it had been floating in the sea for some time, as its bottom was crusted with barnacles and weed. Welded to its upper surface, they discovered, were dozens of skeletons, including humans, monkeys, and two big cats, probably Sumatran tigers.

It was a relic of the eruption of Krakatoa, which had taken place nine months earlier in the Dutch East Indies. The rock had floated 4,000 miles across the Indian Ocean to the east coast of Africa.

(From Simon Winchester’s Krakatoa, 2013.)

This is a familiar variation on the Müller-Lyer optical illusion. The horizontal segments on the left appear longer than those on the right, but in fact they’re all the same length.

Italian researcher Gianni A. Sarcone devised the dynamic demonstration below — the blue and black segments are all the same length and do not change; only the “fins” are moving:

(The Müller-Lyer illusion works even in blind subjects!)

‘I had quite a bit of fun playing hide-and-seek with a squirrel,’ he said. ‘You know that little round glade with a lone birch in the centre? It was on this tree that a squirrel was hiding from me. As I emerged from a thicket, I saw its snout and two bright little eyes peeping from behind the trunk. I wanted to see the little animal, so I started circling round along the edge of the glade, mindful of keeping the distance in order not to scare it. I did four rounds, but the little cheat kept backing away from me, eyeing me suspiciously from behind the tree. Try as I did, I just could not see its back.’

‘But you have just said yourself that you circled round the tree four times,’ one of the listeners interjected.

‘Round the tree, yes, but not round the squirrel.’

‘But the squirrel was on the tree, wasn’t it?’

‘So it was.’

‘Well, that means you circled round the squirrel too.’

‘Call that circling round the squirrel when I didn’t see its back?’

‘What has its back to do with the whole thing? The squirrel was on the tree in the centre of the glade and you circled round the tree. In other words, you circled round the squirrel.’

‘Oh no, I didn’t. Let us assume that I’m circling round you and you keep turning, showing me just your face. Call that circling round you?’

‘Of course, what else can you call it?’

‘You mean I’m circling round you though I’m never behind you and never see your back?’

‘Forget the back! You’re circling round me and that’s what counts. What has the back to do with it?’

— Yakov Perelman, Mathematics Can Be Fun, 1927

From the Strand, July 1903:

The curious photograph which is here reproduced shows the well-known inventor of flying-machines, M. Santos Dumont, perched upon what looks like an abnormally lofty office-stool, accompanied by a friend in a similar position. The reason for this peculiarity lies in the fact that M. Santos Dumont is so accustomed to the sensation of being elevated above the earth that he feels more at home when he is so, even at meal-times.

This sounds like a joke, but the New York Herald tells of a dinner Santos-Dumont held in Paris that year:

From tables seven feet from floor to cloth the viands and wines were served, while the waiters attending to their wants walked about on stilts. The chairs, with their long, thin legs, were reached by mounting a short flight of portable steps.

Industrialist C.K.G. Billings had held a dinner on horseback that March in New York; possibly Santos-Dumont had taken that as inspiration. Here are a few more photos.

In a dream someone said to me, ‘Any general thesis which is put forward without a concrete example is therein badly presented’. That was all he said, and I was about to point out the irony that in merely putting forward this thesis by means of a general statement the speaker had failed his own requirement of providing an example when it suddenly occurred to me, as I exclaimed to him, ‘Ah, I see. Your putting forward this thesis without an example is itself the concrete example’. But when I awoke I realized there was a problem here. If indeed the speaker is credited with having given me a concrete example of an example-less bad presentation, then that credit must be immediately withdrawn, because what he has given me is not an example of an example-less bad presentation. But if it is not an example, then it must once again be received as an example of example-less presentation, but then it once again is not an example, and so on forever.

— Arnold Zuboff, in Analysis, July 1992