Where and How could the Wallace Experiment Easily Be Repeated?

Mick West

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A classic demonstration of the curvature of the Earth was performed by Alfred Russel Wallace in 1870:

http://blogs.scientificamerican.com...modern-biology-got-suckered-by-flat-earthers/
1905_Wallace_A237.2_fig399.jpg
(Original source is Wallace's "My Life", Page 364-376)


Put more simply, we have:

A) A telescope (which we would replace with a digital camera with powerful zoom lens)
B) A target 3 miles away
C) A target 6 miles away, in line with A and B.

A,B, and C are all the same height above the waterline. So you just look from A towards B and C, and if B is visually higher than C then the water surface is curved up in the middle.

Rather surprisingly I can't find any well documented recreations of this experiment. It seems like it would be an ideal science project. There are significant difficulties though as you need a suitable stretch of water, the targets are 12 feet above the water, and the six mile distance makes it difficult to coordinate.

But it's really a very straightforward demonstration. So what I'd like to do in this thread is discuss places where the experiment might best be carried out, and what procedures could be used to make the execution of the experiment as straightforward and foolproof as possible.
 
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Mick West

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One idea to open up more locations would be to use a periscope at point A. You could make quite tall lightweight periscope with very simple cheap construction This gives you a lot more flexibility in terms on positioning the camera and targets.

You could use some 1" PVC Schedule 40, which would also be good for the target supports. You could make a clip-together or telescoping arrangement of the PVC pipe for easy transport, even adjustable heights. It's $4 for a 10' section.
 

Mick West

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A series of three bridges such as in the original seems ideal, as you can use a simple plumb measure to get the height.

The original Bedford Level is still there, and has been used to kind of recreate the useless "man in a boat" version of the experiment. But it's not clear if it's still suitable for the Wallace experiment. These seem to be the bridges:
20160912-141904-gg5f7.jpg (See attached Google Earth File)

However the middle bridge is a railway bridge and does not seem to have access.
 

Attachments

Hama Neggs

Senior Member
A flowing body of water will have a sloped surface. Else it wouldn't be flowing. There has to be some factor figured in for that.
 

Mick West

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Staff member
A really long straight causeway could be a opportunity for multiple targets. Might be tricky though

Seven Mile Bridge, Florida



Pontchartrain causeway, Lousiana
 

Bass In Your Face

Active Member
I live next to this lake. There are 4 possible places to do this, tell me what you think:









The locations of the left hand side from the pictures, from top->down, are:

-A dock/boat loading area
-Beach/boat loading area
-Beach/boat loading area
-A small water inlet with a boat loading area

The right side locations from the pictures, from top->down, are:

-Accessible shore from road, or by boat
-Accessible shore from road, or by boat
-Accessible shore from road/park, or by boat
-Accessible shore from road/park, or by boat

Also, many people ice fish on this lake in the winter.. (and would probably ice fish in the summer if there was ice! Wisconsin!!!)
 

Mick West

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It's hard to get a spot exactly in the middle. At this scale we can approximate the curve as a triangle, and for an offset midpoint at a distance m from the end (where m<d/2), then we can approximate the "bulge" as bulge*2m/d

So for 5 miles, bulge is 4.17 feet, but if the middle marker were at 1.5 miles, then it 4.17*2*1.5/5 = ~2.5 feet.

So a 5 mile span should still work, even if you can't get the middle exactly.
 
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Mick West

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Folsom Lake is plausible. There's a 4 mile stretch with a pretty centered spit of land (depending on the water level)20160912-171849-9vwfr.jpg

The middle is only really accessible by boat though.
 

Mick West

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It's hard measuring from a water surface in a canal, etc. But if you are on a sloping shore, then you can make the targets of fixed pre-measured height with a nice solid base, and simply place them with the base on the waterline. Would need some adjustment for slope though
 

Mick West

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Wallace's correspondence from the time is still relevant now.

http://people.wku.edu/charles.smith/wallace/S179AA.htm
Six miles is a very long way. However I think a P900 or similar would be sufficient. Here is a zoom test of 5km (3.1 miles)
Source: https://www.youtube.com/watch?v=VQPZuBlCvvg

20160913-075328-c554f.jpg
20160913-075450-0390i.jpg

So that's the type of angular resolution and distortion you would get at the midpoint. Sufficient to resolve railings that are likely only an inch thick or less.

The far point, at 6 miles, would be half the size, and with additional atmospheric distortion. Wallace used "a large sheet of white calico, six feet long and three feet deep, with a thick black band along the centre". I'd suggest the same, and based on the above a 3" thick black band. Specifically I suggest using two strips of Gorilla Tape, which besides being black is also very unlikely to fall off the board (and black duct tape could do, Gorilla Tape is more heavy duty). The board itself could be a piece of plywood painted white, or some poster board (might be too fragile), or even an actual dry-erase whiteboard.

I also suggest giving the board a distinctive border with tape, and maybe some colored squares to make it easier to find, like:
20160913-081830-64335.jpg
 
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Trailblazer

Moderator
Staff member
A series of three bridges such as in the original seems ideal, as you can use a simple plumb measure to get the height.

The original Bedford Level is still there, and has been used to kind of recreate the useless "man in a boat" version of the experiment. But it's not clear if it's still suitable for the Wallace experiment. These seem to be the bridges:
View attachment 21345 (See attached Google Earth File)

However the middle bridge is a railway bridge and does not seem to have access.
There are footpaths/bridleways along both sides of the Old Bedford River all the way along: http://streetmap.co.uk/map.srf?x=55...ty/Town/Village]&searchp=ids.srf&mapp=map.srf

Street View suggests that overhanging trees might be a problem, though.

upload_2016-9-13_16-48-45.png


There's also a dead straight 6 mile stretch in the other direction from the Welney bridge to the next bridge:

upload_2016-9-13_16-47-26.png
 
Grand Traverse Bay in Michigan would be a good contender.

There's a peninsula in the middle, and it's at about the halfway point.

For some reason, my computer doesn't want to screenshot it.

Anyway, it's about ten miles from the peninsula near sutton's bay to the mainland, and where the Old Mission Light is is roughly halfway. You could put the targets in water, maybe have them mounted on a 5-gallon bucket filled with concrete, put a 'water level' mark on them wade them out that far, and presto. Easy way to replicate the Wallace experiment, and if you made them ten or twelve feet high, your'd potentially minimize the effects of refaction near the surface.

Now, if you had a boat, you could make floating targets (a tripod supported on three inner tubes) and use your GPS to space them however many miles apart you wanted for the experiment, and you could really do that nearly anywhere on the Great Lakes.
 

Z.W. Wolf

Senior Member
There are quite a few dry lake beds in California and Nevada. How do you tell the surface is exactly level? When the winter rains come along, it's common for a lake bed to be covered with a thin layer of water only inches deep. You can still drive over the lake bed, but on a still day the surface of the water should be a very good gravity equipotential surface.

As for the Bedford Level, I've previously asked people on another forum if there were any UK members interested. I got some casual interest. I'll ask again, more seriously.
 

mowgli

New Member
Am keeping an eye on this.. I am based about 1hr drive from the original Canal. Not sure how involved I can be directly though as lots of family commitments :eek:(
 

Mick West

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So that's the type of angular resolution and distortion you would get at the midpoint. Sufficient to resolve railings that are likely only an inch thick or less.
I just got the same camera, a Nikon P900, mostly for videoing planes, but it's also ideal for earth curvature experiments with a 2000mm equivalent zoom. It's also much more practical that a DSLR with a long lens, as it's much lighter and smaller. Here's an "actual pixels" handheld shot of a gas station awning about 5km (3 miles) away. It's a hot day (around 85°F)

20160928-100140-fnjax.jpg

Here's the same type of gas station
20160927-165952-cezoi.jpg

So you can see you get reasonable contrast with the approx 1 foot blue stripe on a 2 foot white background. The red and blue Arco logo is also reasonably visible.

20160928-100324-w4ycd.jpg
Remember though that the Wallace experiment was twice as far as this, so this represents a bit past the midpoint.
 
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Mick West

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It was a bit hot for the time of year here. I'll try taking photos of the same scene and recording weather conditions, to see what the effect is. There's some varied weather coming.

20160927-173346-8hmpm.jpg
 

Trailspotter

Senior Member
I'll try taking photos of the same scene and recording weather conditions, to see what the effect is.
You also can try taking short HD videos of the scene. Although there will be fewer pixels per frame, by going through the video frame-to-frame, it is possible to find a frame with a sharper image than in a single still photo. I found this trick helpful when trying to read the tail number of a distant aircraft.
 

Mick West

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You also can try taking short HD videos of the scene. Although there will be fewer pixels per frame, by going through the video frame-to-frame, it is possible to find a frame with a sharper image than in a single still photo. I found this trick helpful when trying to read the tail number of a distant aircraft.
I took a short video of the freeway about 300 feet from the gas station. Like you say there are occasional moments of clarity from the camera movement and the heat haze (turbulent atmospheric refraction)

Source: https://www.youtube.com/watch?v=ihn9kANb5Qo


A tripod will help :) But I think it's clear that a midpoint target need only be around 1 foot in diameter, providing it is of sufficiently high contrast (like a red disc).
 

Mick West

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Although, shot this early morning so I could see the gas station lights. Did not come out incredibly well handheld

20160928-100535-6tgfj.jpg

Still, the strip of blue lights are quite distinguishable.
 
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Trailspotter

Senior Member
A tripod will help :) But I think it's clear that a midpoint target need only be around 1 foot in diameter, providing it is of sufficiently high contrast (like a red disc).
Actually, I was thinking about the noise reduction by taking multiple images of the same scene (with help of a tripod mounted camera) and averaging them. Taking a video probably is the easiest way of doing it. There may be burst and continuous shooting options, but they require holding the shutter button that may cause the camera drift.
 

Mick West

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Actually, I was thinking about the noise reduction by taking multiple images of the same scene (with help of a tripod mounted camera) and averaging them. Taking a video probably is the easiest way of doing it. There may be burst and continuous shooting options, but they require holding the shutter button that may cause the camera drift.
That's in interesting idea, I know you can increase effective resolution, as explained here:
http://petapixel.com/2015/02/21/a-practical-guide-to-creating-superresolution-photos-with-photoshop/
However there's some suggestion it might not work well with atmospheric distortion.
http://www.cambridgeincolour.com/forums/thread44497.htm#post492514
I'll tripod the camera and give it a go.
 

Mick West

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So I'm trying to figure out best time of day. Here's a shot at first sunlight:
20160928-100803-y3v2d.jpg
Still rather a lot of atmospheric distortion. It was about 70°F/21°C
 
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Mick West

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Overcast days seem best. Pity about where you live..
Yes it's terrible here. Warm and sunny all the time, and worst of all, no contrails for the last two months!!

Overcast would be ideal as there would be basically no heating of the ground, greatly reducing convection turbulence. Maybe later in the week.
 

Mick West

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Well, a tripod and more sunlight made an astonishing difference, 9:20, around 80°
20160928-100941-8pw56.jpg

That's on a tripod with manual shutter release (i.e. I pressed the button) and image stabilization on

Compare with yesterdays afternoon handheld


Note the difference in the red and blue signs. Barely visible in the older shot.
 
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Mick West

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I suspect a large part of the reason why the above image is so good is the closeness of air temperature and ground temperature.

Outside right now, measure the shaded air temp at 76 and the ground temp at 72 (using a Thermopen meat thermometer both in soil and an unheated spa). The sun has not yet heated the ground sufficiently to cause it to warm the air above it (and create convection).
 

Trailblazer

Moderator
Staff member
Well, a tripod and more sunlight made an astonishing difference, 9:20, around 80°
View attachment 21695

That's on a tripod with manual shutter release (i.e. I pressed the button) and image stabilization on
I can't quite tell from the crop, are those wires at the gas station (or at least close by)? That's pretty incredible to be able to pick out individual utility cables from 5km away.
 
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