Ernest Rutherford related the following story:

Some time ago I received a call from a colleague. He gave student a zero for his answer to a physics question, while the student claimed a perfect score. The instructor and the student agreed to an impartial arbiter, and I was selected.

I read the examination question: "Show how to determine the height of a tall building with the aid of a barometer." The student had answered: "Take the barometer to the top of the building, attach a long rope to it, and lower it to the street; the length of the rope is the height of the building."

The student really had a strong case for full credit since he had answered the question correctly! On the other hand, the answer did not prove the student's competance in physics.

I suggested that the student have another try. I gave the student six minutes to answer the question with the warning that the answer should show some knowledge of physics. After five minutes, he hadn't written anything. I asked if he wished to give up, but he said he had many answers to this problem; he was just thinking of the best one. I excused myself for interrupting him and asked him to please go on.

In the next minute, he wrote his answer, which read: "Take the barometer to the top of the building and lean over the edge of the roof. Drop the barometer, timing its fall with a stopwatch. Then, using the formula x=0.5*a*t^2, calculate the height of the building." At this point, I asked my colleague if he would give up. He conceded, giving the student full credit.

While leaving my colleague's office, I recalled that the student said he had other answers, so I asked what they were. "Well," said the student, "there are many ways of getting the height of a tall building with a barometer. For example, you could take the barometer out on a sunny day and measure the height of the barometer, the length of its shadow, and the length of the shadow of the building, and using proportions, determine the height of the building."

"Fine," I said, "and others?"

"As you climb the stairs, you mark off the length of the barometer along the wall. You then count the number of marks, and this will give you the height of the building in barometer units."

"You can tie the barometer to the end of a string, swing it as a pendulum, and determine the value of g [gravity] at the street level and at the top of the building. From the difference between the two values of g, the height of the building, in principle, can be calculated."

"Finally," he concluded, "there are many other ways of solving the problem. Probably the best is to take the barometer to the building's superintendant and say: 'Here is a fine barometer. If you tell me the height of this building, I'll give you this barometer."

At this point, I asked the student if he really didn't know the conventional answer to this question. He admitted that he did, but said he was tired of instructors trying to teach him how to think.

The student was Niels Bohr.