This legend, the truth of which is not necessarily related to its value,
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: "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
This highly original answer so incensed the examiner that the student was failed
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 pres- sure 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 building."
The student was Niels Bohr, the only Dane to win the Nobel prize for Physics.