Using a barometer, how high is this tower?

Let's see some suggestions - I'll start with some obvious ones:

1) find the architect and say 'Tell me how high the tower is and I'll give you this fine barometer'

2) use the barometer as a measuring stick

3) stand the barometer in the shadow of the tower and use the principle of equal triangles

4) make the barometer the bob of a pendulum and calculate the height from the period of the pendulum

5) drop the barometer from the top of the tower and count (followed by a lengthy period of barometer parts retrieval)

6) put the barometer on ebay and buy a tape measure

I think you've raised the bar on this occasion Neil.







Where's the bar?




Judging by the December Saturday nights I've seen in Carlisle over the years most folk would fail a barometer test.

Aren't a barometer and a pressure altimeter the same thing?

What's the barometer measuring in, inHg?

You could always subtract the pressure readings from top and bottom of the tower but I guess you'll need temperature too to be anywhere near mildly accurate.

Yes, just different dials but they work on the same principle, measuring atmospheric pressure.

Commission the the largest barometer ever built - the size of the tower, and get them to send over the specs. Lunch.

Unfortunately by the time you've ascended the tower to take reading number two (assuming reading number one at the base) odds are that atmospheric pressure will have varied naturally anyway, introducing error on the comparative result.

Whilst recognising Ignoring the issues of gravity You'd need two barometers to relate to each other, leave one at the tower base and take one up with you, and take readings at specific identical times before doing the appropriate calculations.
And you'll need two watches or other timing devices as well !!!

Here's two: weigh the barometer at ground level, and weigh it again at the top of the tower; use the change in weight to calculate the gravity and therefore the distance from the centre of the earth.

Or, in a similar vein, use the barometer as a pendulum, measure the period, take it to the top and observe the difference in period; again, this tells you the gravity at the top and the bottom.

JohH, if you choose a calm sunny high-pressure day, you'll find that the pressure is likely to change by only fractions of a millibar over the course of the day. The rate of change of pressure with altitude is much greater.

(For what it's worth, I have an aneroid barometer on the wall which was made in 1917 and is quite capable of noting the pressure difference between the floor and the ceiling. According to it, Hemel moves up and down by several hundred feet from time to time!)

Are you re-measuring St Mary's spire Neil?

Ah, but if all you have is a barometer and the tower, how do you propose measuring the period of the pendulum.....or indeed tie it to anything?

Agreed the differance in fractions of millibars is small but it depends how accurate you a want the height to be determined.
And gravity is affected by earth tides so again time differances in measurements can make a differance to the final calculated figures. It sucks !

Well, I guess we'd better hope that it's a mercury barometer from which we can McGyver a laser rangefinder...

The change of pressure with height, close to sea level, is around 27mmHg/1000ft - call it 0.1mBar/meter. It slows down as you get higher; there's less air sitting on top.

Go up the tower with the barometer and a high speed camera. Wait till some smartarse yells "What's the weather like up there?". Record the whole thing on the camera and then analyse the time delay between the audio and video.