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> Now David Last year my vacation project was a potato cannon. This is definitely a candidate for 2007. JS ----- Original Message ----- From: "David & Alison Webster" <dwebster@glinx.com> To: <NatureNS@chebucto.ns.ca> Sent: Thursday, February 08, 2007 4:26 PM Subject: Re: [NatureNS] Determining Elevation the hard way > Hi Steve & All, Feb 8, 2007 > It is curious how one question will often disclose the answer to > another question. Jamie's question has solved the Oak Island mystery. i.e. > the so-called money pit shaft was dug by a coconut-mat salesman who > wondered how high his house was above sea level and had only a shovel and > a rope for tools. > > Your formulation looks good but I would expect instrument error to be > large & have consequently looked at a second approach; an improvized > differential water manometer. At least that seems like a reasonable name. > Having never used or made anything similar, it would be best to check this > method out before using it to establish runway elevation for instrument > landing purposes. > > Theory: This procedure makes use of the change in air pressure with > elevation. At the initial elevation (house or mean sea level as > convenient) water height in a transparent U-tube (both arms the same) is > recorded just after one end is closed to the air such that air volume of > the closed end is not changed. As rapidly as possible (to avoid > temperature changes) the unit is moved to the other location (mean sea > level or house) and the height of water in the two arms is recorded. If > the initial point is not about half way between the two final points then > there has been a change in water volume or enclosed air volume due to > temperature changes and it may be desirable to start again. As a rule of > thumb, a 5 cm difference from sea level would represent an elevation > difference of about 3.9 metres. > > [DIGRESSION: If I have thought this through correctly, the difference > in water level between the two arms will slightly or seriously > underestimate the difference in air pressure between the two locations, > because change in volume of the air on the closed side will change air > pressure on the closed side. A smaller air pressure on the closed will be > increased and a larger pressure on the closed side will be decreased by an > amount proportional the fractional change in volume. It might be possible > to correct for this it one had to. ] > > From observed difference (h; cm) in water level between the two arms > (ignoring the bias described in DIGRESSION) and assuming a temperature of > 4o C, one can estimate Z, elevation (cm) above mean sea level using > > Z= (ln po- ln p)RT/g > > where ln is natural log, po is pressure in dynes/cm^2 at sea level > (1,013,250), p is pressure at the house (1,013,250 -(h x 980)), R is 2.87 > X 10^6, T is 277o K and g is 980. > > Materials: One McGyver scrap pile, or considering component parts, a > valve stem from a bicycle innertube, pine board about 3" wide and 8' long > or equivalent (hinged or in two sections so it will fit in a car), duct > tape, tacks, about 6' of 5/16 ID tygon tubing, hot water bottle with enema > tube, ruler or metre rod secured to middle of board at eye level, rabbit > wire, nail, spring clamp & calculator. > > Preparation & Construction: Wash the inside of the tygon tube > thoroughly with hot water and dish detergent, heat one end in near boiling > water, spread if necessary using a tapered stick and insert the valve stem > (previously cut from the inner tube) business end out. Moistening the tube > with glycerine will help. > Boil several cups of water for at least 2 minutes (to remove dissolved > air), add a drop of dish detergent and pour into the hot water bottle > quickly but avoid entrained air (e.g. by funnel with bottle suspended in > cold water), purge any air trapped from the bag corners, tighten enema > tube stopper, fill enema tube with water slowly from below and store in > fridge after cooling in cold water. Ideally, to avoid fussy temperature > adjustments, the water should be at about 4o C when used and measurements > should be taken when weather is about 4o C. > Secure valve stem end of tube above board end using duct tape and > tacks. The tube section at ruler level should lie near the ruler edge. > Fasten rabbit wire to the other end to facilitate water addition. Remove > valve stem insert entirely or have it very loose and add water to wire end > of tube from below using the enema tube and water bottle. Adjust water > level to near middle of ruler, wrap wire of wire end over nail & clamp > wire to board. Tighten valve stem insert and press pin in gently, if > necessary, so pressure (water level) of the two arms is equalized. > As described previously, record water level, move quickly to the second > location and record level in the two arms. > > For elevations above sea level up to 10 to 15 feet this might work > fairly well. Do try this at home (basement to attic) and let me know what > happened. > > Yours truly, Dave Webster, Kentville > > > > > > Steve Shaw wrote: > >> Y >> ........................................................................ >> .<...................> house level >> | . , >> | . , >> | . , >> H . , >> | . , >> | . >> , >> | . , >> 0末末末末末帽1末末末末末乏1末末末末末帽2末末末末末R2 >> >> < - flat beach level -> >> I agree with Paul, you need a GPS but also at least one angle; but, if >> you must try to do it the hard way: >> In the diagram above (hoping it doesn't wrap-around on your monitor >> display) your house is at 'Y', at height 'H' above beach level, which >> projects vertically down below you to point '0' at beach level. >> Tools: get out your builder's spirit level (set it up horizontally) and >> your telescope, and duct tape a straight stick to the telescope to use >> as an angle pointer. Set the telescope exactly horizontal, then rotate >> it downwards to focus on a nice prominent beach rock visible on your >> beach at 'R1'. Measure the angle of declination (rotation) with a >> simple protractor, then calculate (90-this angle), to finally get a >> number for the angle (0-Y-R1) = call it angle A1. >> Re-level the telescope and rotate it down again to focus it on a more >>