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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lord Kelvin's lunars game (and an old joke)
From: Lu Abel
Date: 2005 May 27, 08:42 -0700
From: Lu Abel
Date: 2005 May 27, 08:42 -0700
In a similar vein, there's an apocryphal story about physicist Neils Bohr (awarded the Nobel Prize for his invention of quantum mechanics). On an examination, he was asked how to determine the height of a building using a barometer. The obvious answer is to determine the difference in barometer readings at the bottom and top of the building and use the difference to calculate the change in altitude, much like the workings of an aircraft altimeter. Bohr, brilliant and bored, decided to give a whole bunch of answers, carefully avoiding the obvious and expected one: 1. Tie a string to the barometer, lower it from the top of the building until it almost touches the ground, swing it like a pendulum, and measure its period. 2. Drop it and count the seconds until it hits the ground. 3. Set the barometer down next to the building and measure the length of its shadow and the length of the building's shadow; the heights of the two have the same ratio as the length of their shadows. 4. Walk up the stairs carrying the barometer, marking off its length up the wall, thereby using it as a ruler to measure the height of the building in "barometers." 5. As a variant of #1, tie the barometer on a fairly short length of string. Measure the period of the resulting pendulum at both the bottom and the top of the building. Since the force of gravity varies with altitude, the height of the building can be calculated from the change in the period of the pendulum. 6. As another variant of #1, set up the long pendulum of #1 and measure its precession. 7. Last but not least, the method guaranteed to get the most accurate answer: Go to the basement of the building. Knock on the custodian's door. Say to him "I'll give you this really fine barometer if you'll tell me the height of the building." Lu Abel