In every work of genius, we recognize our once rejected thoughts.

The barometer exercise sets a trap for you. It is a complex instrument that measures pressure. We know that height is related to pressure - so there is a way to measure height using a barometer. This is likely to be the first answer that you come up with. There was once a physics student who was asked this question during an exam. The student was a rebellious sort and decided to explain several 'unconventional ways in which the height of a building could be measured with the barometer. He was fed up being told how he should think. He failed the question and appealed, saying that his answer was just as good as the 'correct answer' The examiners finally accepted that his answer was valid.

The point is that there are always several solutions to a challenge. But 'invisible rules' can prevent us from seeing them - we are not as free in our thinking as we may think.

The most exciting phrase to hear in science - the one that heralds new discoveries - is not "Eureka!" but "That's funny..." (Isaac Asimov)

We have already said that we could compare the difference in air pressure between the ground and the top of the building to determine its height. Other possibles are:

Shadows - Measure the length of the shadows of the barometer and the building, calculate the proportional ratio

Competition - Offer the barometer as first prize in a 'guess the height of the building' competition.

Gravity Use a Helicopter to get to 10,000 feets (or someway above the building). Drop the barometer and time the drop. Using the appropriate maths work out that distance and then calculate the building height.

Perspective - Measure the length of the shadows of the barometer and the building, calculate the proportional ratio

Extrapolation - Tie the Barometer to a thread. Go to the First Floor and release the thread through the window until it touches the Ground. Calculate how many "barometer lengths" make up the height of one floor, and multiply this by the number of floors.

Linear measurement - Attach the barometer to the end of a long rope, climb the building, lower the barometer to the ground, then measure the length of the rope.