This concerns a question in a physics degree exam at the University of
Copenhagen: "Describe how to determine the height of a skyscraper with
a barometer."

One student replied: "You tie a long piece of string to the
neck of the barometer, then lower the barometer from the roof of the
skyscraper to the ground. The length of the string plus the length of
the barometer will equal the height of the building."

This highly original answer so incensed the examiner that the
student was failed immediately. He appealed on the grounds that his
answer was indisputably correct, and the university appointed an
independent arbiter to decide the case. The arbiter judged that the
answer was indeed correct, but did not display any noticeable knowledge
of physics. To resolve the problem it was decided to call the student
in and allow him six minutes in which to provide a verbal answer which
showed at least a minimal familiarity with the basic principles of physics.

For five minutes the student sat in silence, forehead creased
in thought. The arbiter reminded him that time was running out, to
which the student replied that he had several extremely relevant
answers, but couldn't make up his mind which to use. On being advised
to hurry up the student replied as follows:

"Firstly, you could take the barometer up to the roof of the
skyscraper, drop it over the edge, and measure the time it takes to
reach the ground. The height of the building can then be worked out
from the formula H = 0.5g x t squared. But bad luck on the barometer.

"Or if the sun is shining you could measure the height of the
barometer, then set it on end and measure the length of its shadow.
Then you measure the length of the skyscraper's shadow, and thereafter
it is simple matter of proportional arithmetic to work out the height
of the skyscraper.

"But if you wanted to be highly scientific about it, you could
tie a short piece of string to the barometer and swing it like a
pendulum, first at ground level and then on the roof of the skyscraper.
The height is worked out by the difference in the gravitational
restoring force T = 2 pi sq root(l / g).

"Or if the skyscraper has an outside emergency staircase, it
would be easier to walk up it and mark off the height of the skyscraper
in barometer lengths, then add them up.

"If you merely wanted to be boring and orthodox about it, of
course, you could use the barometer to measure the air pressure on the
roof of the skyscraper and on the ground, and convert the difference in
millibars into feet to give the height of the building. But since we
are constantly being exhorted to exercise independence of mind and
apply scientific methods, undoubtedly the best way would be to knock on
the janitor's door and say to him 'If you would like a nice new
barometer, I will give you this one if you tell me the height of this
skyscraper'."

The student was Niels Bohr, the only Dane to win the Nobel
prize for Physics.

.....From the New Scientist Compendium, issue 4. ...Back to Index