A Confusing Census

There are 12 people in a room. Some always tell the truth, and the rest always lie.

#1 says, “None of us is honest.”
#2 says, “There is not more than 1 honest person here.”
#3 says, “There are not more than 2 honest people here.”
#4 says, “There are not more than 3 honest people here.”
#5 says, “There are not more than 4 honest people here.”
#6 says, “There are not more than 5 honest people here.”
#7 says, “There are not more than 6 honest people here.”
#8 says, “There are not more than 7 honest people here.”
#9 says, “There are not more than 8 honest people here.”
#10 says, “There are not more than 9 honest people here.”
#11 says, “There are not more than 10 honest people here.”
#12 says, “There are not more than 11 honest people here.”

How many honest people are in the room?

Click for Answer

You Are There

Prague artist Robert Barta’s installation Crossing Half a Million Stars consists of 500,000 ball bearings covering the floor of a room.

The visitors themselves create a spontaneous performance as they try to make their way across it.

“Pussy and the Mouse”


A puzzle by Henry Dudeney:

‘There’s a mouse in one of these barrels,’ said the dog.

‘Which barrel?’ asked the cat.

‘Why, the five-hundredth barrel.’

‘What do you mean by the five-hundredth? There are only five barrels in all.’

‘It’s the five-hundredth if you count backwards and forwards in this way.’

And the dog explained that you count like this:

1     2     3     4     5
9     8     7     6
     10    11    12    13

So that the seventh barrel would be the one marked 3 and the twelfth barrel the one numbered 4.

‘That will take some time,’ said the cat, and she began a laborious count. Several times she made a slip, and had to begin again.

‘Rats!’ exclaimed the dog. ‘Hurry up or you will be too late!’

‘Confound you! You’ve put me out again, and I must make a fresh start.’

Meanwhile the mouse, overhearing the conversation, was working madly at enlarging a hole, and just succeeded in escaping as the cat leapt into the correct barrel.

‘I knew you would lose it,’ said the dog. ‘Your education has been sadly neglected. A certain amount of arithmetic is necessary to every cat, as it is to every dog. Bless me! Even some snakes are adders!’

Now, which was the five-hundredth barrel? Can you find a quick way of arriving at the answer without making the actual count?

Click for Answer

Oh Well


In 1913 Canadian politician Sam Hughes proposed the MacAdam Shield Shovel, a spade that could double as a protective shield in the trenches — it was provided with a hole through which a soldier could survey the enemy.

Some 20,000 had been manufactured before it was discovered that the blade was not remotely bulletproof, and it wasn’t much use as a shovel … because there was a hole in it.

The Frog Battery


Early experimenters in electricity sometimes dealt in frogs’ thighs. Dissecting a frog creates an “injury potential” in its muscles, which can then be arranged in series to produce a kind of biological battery. Carlo Matteucci strung together 12 to 14 half-thighs to make a “frog battery” strong enough to decompose potassium iodide; he was able to induce some effect even with living frogs.

Matteucci did similar work with eel, pigeon, and rabbit batteries. In 1803 Giovanni Aldini used a galvanoscope made of frogs to detect current in a circuit that ran from an ox’s tongue to its ear through Aldini’s own body. The mechanisms underlying these results weren’t always clearly understood, but they formed important early strides in bioelectrochemistry.

Maps and Symbols

Image: Wikimedia Commons

This map shows mountain symbols above a river symbol. Suppose that, in the part of the world that the map represents, there really are mountains in the location that the map indicates. But suppose that there are also mountains on the other side of the river — where no mountains are indicated on the map. Would we say that the map is inaccurate?

People tend to say yes — in general, if a marker appears on a map, then we tend to think that the absence of the marker reflects an absence of that feature from the corresponding location.

But this is very different from linguistic representation. “After all,” writes Rutgers philosopher Ben Bronner, “if I say that there are mountains north of the river, the accuracy of my assertion doesn’t depend on whether there are mountains south of the river.”

And suppose I drew a map on which some national capitals were indicated, but not all. We wouldn’t take this to mean that the absent capitals don’t exist, merely that the map is incomplete. So how can we make sense of the intuition?

(Ben Bronner, “Maps and Absent Symbols,” Australasian Journal of Philosophy 93:1 [2015], pp. 43-59.)


Image: Wikimedia Commons

The town of Bozouls in the south of France sits at the edge of a horseshoe-shaped canyon 300 feet deep, the product of 2 million years of erosion of the region’s limestone plateau by rivers and glaciers.

Because the outcrop at the center of the horseshoe is accessible only from the south, it makes an ideally defensible position, and a castle was built there in the 9th century, of which only ruins remain. In medieval times guards in towers monitored the approach 24 hours a day.

One historic building still survives: The 12th-century St. Faustus church sits right on the edge of the cliff, looking over the river.

A Shocking Experience

On a dry summer day in California, physicist Julius Sumner Miller was driving slowly near the desert when a friend overtook him on the left. The friend’s wife, in the passenger seat, reached out to hand him a package of gum. Their hands were no less than 3 inches apart when “a terrific discharge took place which possessed the classical physiological effects. The shock was momentarily disabling, as a three-inch spark in air can well be.”

Miller published an inquiry about this in the American Journal of Physics and received a reply from R.F. Miller of B.F. Goodrich in Ohio. The motion of the cars had built up charges of different amounts; Goodrich had found that the accumulated charges can (or could) increase greatly as the wheel rotates, and “as soon as the tread charges are far enough removed, they will find a lower resistance path through the rim to ground rather than around the tread,” charging the vehicle.

Even at the time the phenomenon was well known; in his original letter Miller noted that gasoline trucks were required by law to carry a dragging chain or strap. But “the question as to how great a charge may accumulate is difficult to answer.”

(Julius Sumner Miller, “Concerning the Electric Charge on a Moving Vehicle,” American Journal of Physics, 21:4 [April 1953], 316.)



The Treaty of Versailles contains a macabre clause:

ARTICLE 246. Within six months from the coming into force of the present Treaty, … Germany will hand over to His Britannic Majesty’s Government the skull of the Sultan Mkwawa which was removed from the Protectorate of German East Africa and taken to Germany.

Mkwawa was a tribal leader in German East Africa who opposed colonization. After his defeat in battle, the Germans had sent his skull to Berlin. When the United Kingdom inherited the colony after World War I, the British sought to return the skull to the Wahehe people, but there was some confusion as to its whereabouts. It wasn’t actually returned until 1954, when Tanganyika governor Sir Edward Twining tracked it down in the Bremen Museum. It now resides at the Mkwawa Memorial Museum in Kalenga, Tanzania.

(Thanks, Jon.)