F-factor
Q: The following recently made its way into the New 杏吧原创office鈥�
Please read this sentence and count the Fs:
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FINISHED FILES ARE THE RE-
SULT OF YEARS OF SCIENTIF-
IC STUDY COMBINED WITH
THE EXPERIENCE OF YEARS.
How many did you see? On first reading most people see only three. However,
the answer is actually six. Why is this?
(continued)
A: Your correspondent will be pleased to know that English is my second
language (Taiwanese is my first) and I am due to take maths A-level exams this
summer. My F count on first reading was three, and it was still three after
seeing the answer. I only realised that the additional Fs were in 鈥渙f鈥� when I
spelt it all out aloud. In fact, I only realised as I recited the second 鈥淥. F.鈥�.
It is my belief that your background has no bearing on whether you spot the
Fs or not. My training as a systems analyst should help me to concentrate on the
task in hand (counting the Fs). As to why I missed them, two explanations
remain. Either it was too late at night or I am obviously not suited to doing a
maths degree and should contemplate a change of course.
Alex Lu
Edinburgh
A: As a postscript I submit the following:
THE
SILLIEST
MISTAKE IN
IN THE WORLD
When trying to persuade a class of seven-year-olds of the need to reread what
they had written, I put the above legend on the blackboard. My best readers
immediately read it as 鈥淭he silliest mistake in the world鈥� and I replied,
鈥淵ou鈥檝e just made it.鈥� It was only when we reached the slower readers that the
extra 鈥淚N鈥� was discovered. At this point the headmaster came into the room,
glanced at the board, and read the message aloud, but incorrectly. A chorus form
the class greeted him: 鈥淵ou鈥檝e just made it, sir.鈥�
The F and V confusion that was suggested by one of your correspondents cannot
be the explanation here.
Douglas Boote
Stockport, Cheshire
Paws for thought
Q: Why do cats love eating fish when they must have evolved without being
likely to encounter them in the wild?
A: The common house cat (Felis domesticus) likes fish because in its
wild state as a marsh dweller of the Nile Valley it did eat fish, along with
frogs, birds and rodents. Its tendency to catch and eat rodents inspired early
Egyptians to (partially) domesticate these natural fish fanciers.
Lou Cameron
New York
A: The Greek historian Diodorus Siculus (80-20 BC), when describing the
sacred animals of Egypt, wrote, 鈥渨hile for the cats and ichneumons [mongoose]
they [the attendants in charge of the animals] break up bread and milk and
calling them with a clucking sound set it before them, or else they cut up fish
caught in the Nile and feed the flesh to them raw鈥�.
There is a distinct possibility that the ancestry of all domestic cats goes
back, at least in part, to the cats of ancient Egypt and, if so, today鈥檚 cats
have had plenty of time to become accustomed to eating fish, and indeed to
drinking milk鈥攁n equally improbable diet for an adult cat.
Juliet Clutton-Brock
Fen Ditton, Cambridgeshire
A: Cats in the wild did catch fish. Domestic cats still do, from uncovered
fish tanks and fishbowls. A young cat next to a shallow river or stream where
fish can be seen swimming gets very excited, and will try to catch the
fish鈥攖he behaviour is innate. They catch them with one front paw and throw
them over their shoulders on to the bank.
This is a common pattern of play in kittens. Although they can catch fish,
young cats are always surprised that water is cold and wet鈥攁nd most
domestic cats never get round to learning this. If they had to survive on fish
in the wild, they鈥檇 learn pretty quickly. Cats are also good, if reluctant,
swimmers. But while this answers your question, it doesn鈥檛 explain why my cat is
passionately fond of crisps, yoghurt and rubber bands.
Edward Barrow
London
Water baby
Q: What is the variation in human body density? Are good swimmers less dense
than average and do denser people invariably make poor swimmers? Please help
explain why I sink as an adult, whereas as a boy I floated endlessly.
A: The densities that you need to know are (in kilograms per litre): bone
1.80; muscle 1.05; fat 0.94; water 1.00; air (lungs) 0.
These combine to a density for an average person of slightly less than the
density of water. Muscular people and skinny people have high densities and are
poor floaters. Women typically contain more fat than men鈥攖hey have lower
densities鈥攁nd are good floaters.
Competitive swimmers, especially men, tend to be tall and thin. They are
actually denser than average. Many can鈥檛 float if totally passive. But they have
an extraordinary 鈥済rasp of the water鈥� and can, just by very small hand
movements, keep afloat.
The density of salt water is slightly greater than for fresh. So switching
from fresh to salt water instantly improves buoyancy. Indeed swimming in
salt water, all other things being equal, turns out to be slightly faster.
In swimming as opposed to comparable land sports, the performance of women is
closer to that of men, because of the greater buoyancy of women. So buoyancy is
a factor in swimming, although a rather insignificant one. Much more important
factors are 鈥済rasp of the water鈥�, low resistance, strength, endurance and water
free from waves and turbulence.
The transition from boy to man is, among other things, a transition to a
higher density, so it is perfectly normal for you to lose your floating ability.
But don鈥檛 despair. Your lack of buoyancy can be cured by an excessive high-fat
diet combined with physical inactivity. This won鈥檛 make you a better swimmer,
though.
Bj酶rn Hee
Arhus, Denmark
This week鈥檚 questions
Dirty old bugs: Do bacteria age? What is the longest-lived single
bacterium?
Pete Kelly
Oxford
Klingoff: Why doesn鈥檛 clingfilm cling to a metal bowl as well as it does to
an equally smooth glass or ceramic one?
Tim Bloomfield
Letchworth, Hertfordshire
Blind blow: Why do we close our eyes when we sneeze?
Bridget Perez
By e-mail, no address supplied