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Determining Elevation
A friend came into the office asking about determining elevation by using boiling water. He said he had heard it was done by the original government surveyors. Not being that old myself, I was not aware of the process, but I understood the theory behind the idea. I was wondering if anyone had any information on the process used or could lead me to any references for the process. I would like to pass the information on to my friend and gain the knowledge for myself. Thanks.
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9 Replies
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My first reaction is that with any thermometer you are likely to find outside a standards lab, you would get very coarse elevations. I found this quote:
“With each 500-feet increase in elevation, the boiling point of water is lowered by just under 1 ?øF.“ Do you have a thermometer that reads in thousandths of a degree?
A quick search finds that 50 microdegree C resolution with 200 microdegree accuracy might be obtainable in a lab, and that corresponds to about 0.18 ft. That, of course, would need corrections for barometric variations and humidity.
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I would say for early exploration mapping, 500’+/- may be a close enough reference frame. Plus you would also be recording temperature and you were boiling water for coffee, tea or dinner. The only effort would be in the measuring and recording.
Paul in PA
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The first explorers to the South Pole used this method to determine the elevation. And then hopefully had a cup of tea.
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Bill, that was my reaction also. They would have to have a very accurate thermometer and hydrometer as I would think it is also affected by the atmospheric pressure. My friend said a picture showed the crew holding a tube. I’m thinking maybe it held a thermometer, drawing sheets or both. Maybe they had a graph of temp. to elevation.
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The barometric variations would be the big correction. If you don’t have a simultaneous reading at a reference elevation, you would get huge variations in computed elevation.
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https://en.wikipedia.org/wiki/Hypsometer
Scroll down to Pressure Hypsometer
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Iced, no doubt..
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I can remember deriving profiles for rural water line construction plans with a precise barometric altimeter. Actually two instruments.
One barometer was set at a fixed location (usually the planned location of the standpipe) with a bonehead (usually me) recording the pressure every fifteen minutes. Trust me, it usually didn’t vary much.
The crew would then traverse (drive…we worked for a cheap engineer) the planned waterline route with an altimeter set with the same barometric pressure. We basically noted elevations in pencil on quad sheets, borrowing from the graphic topography for our location. The crew would regularly return to the base to maintain synchronicity with the base barometer.
I was surprised at the accuracy of most of our ‘survey’. We were definitely doing better than the 10′ intervals on the quad sheets. But hey, it was just a lousy rural water system. I’m sure everybody had good pressure at the tap when it was all said and done!
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Well, you are not going to be measuring elevations to the 0.1′ with boiling water, but thermometers that were accurate to a tenth of a degree F were readily available from around 1835.
The effect on weather systems to barometric pressure pales in comparison to the effect of elevation, especially at higher elevations. So you can make a pretty good topographic map with elevations determined from the boiling point of water, but I wouldn’t try to map a flood zone with a teapot.
A relatively cheap candy thermometer can get you close to 100′ if you don’t try to do it when a major weather system is moving through.
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