1. Rowbotham discusses Theodolite Tangent here: http://www.sacred-texts.com/earth/za/za45.htm
6. Bobby personally performed this sort of water experiment himself and can tell you how sensitive and complex this seemingly simple experiment is. He decided to abandon it. Read his thread: https://forum.tfes.org/index.php?topic=9492.0
1. Rowbotham discusses Theodolite Tangent here: http://www.sacred-texts.com/earth/za/za45.htm
6. Bobby personally performed this sort of water experiment himself and can tell you how sensitive and complex this seemingly simple experiment is. He decided to abandon it. Read his thread: https://forum.tfes.org/index.php?topic=9492.0
1. Rowbotham is only useful as an example of how to bamboozle simple folk with mindgames and twisted logic.
6. The water level equpiment is more than accurate enough for purpose.
As any surveyor should understand, all measurements are in error. We try to minimize error and calculate reasonable tolerances, but error will always be there. Not occasionally; not frequently; always. In the interest of more accurate measurements, we look for better instruments and better procedures.
But, like I say, "accurate enough".
We're not trying to split the atom here, Tom, or perform brain surgery - if that were the case I'd agree, a theodolite or a homemade water level isn't going to be precise enough, or the right tool for the job.
But when it comes to sufficiently measuring "eye level", they do just fine.
If you can show otherwise - I don't just mean "say otherwise" - then go ahead and do so.
But in the absence of that, all you're doing is blowing hot air.
Cheers. :)
I'll just say one last time that they are accurate enough.
Be sure to calibrate it right: bloody difficult, I found.
I see that you yourself made a remark to Bobby on his latest experiment idea:There is a large difference between trying to measure something with a phone and measuring it with tools that architects have been using for centuries.Be sure to calibrate it right: bloody difficult, I found.
Yet we are supposed to assume that all elements in the leveling devices in your examples are "good enough"?
I see that you yourself made a remark to Bobby on his latest experiment idea:Be sure to calibrate it right: bloody difficult, I found.
Yet we are supposed to assume that all elements in the leveling devices in your examples are "good enough"?
You are making threads that we need to change our Wiki or theories because of it?
Be sure to calibrate it right: bloody difficult, I found.
Best way seemed to be at sea level and set it to zero with the horizon there.
It may not give you perfectly accurate angles, but it will reflect perfectly that the angle you look down to the horizon at increases in tandem with your elevation.
I'll just say one last time that they are accurate enough.
As was Bobby's statement leading up to the end. Towards the end of the thread someone posted a video and link to some maths for how small the horizon would actually dip on a Round Earth for the altitude and Bobby remarked that if he had seen the video he may not have even bothered with the experiment.
Your proofs are not well researched and there is no teardown to verify accuracy. At least Bobby was there and willing to verify the elements of the experiment in honesty; which is commendable.
I'll just say one last time that they are accurate enough.
As was Bobby's statement leading up to the end. Towards the end of the thread someone posted a video and link to some maths for how small the horizon would actually dip on a Round Earth for the altitude and Bobby remarked that if he had seen the video he may not have even bothered with the experiment.
Your proofs are not well researched and there is no teardown to verify accuracy. At least Bobby was there and willing to verify the elements of the experiment in honesty; which is commendable.
Hmm, not correct there Tom, I am sure Bobby will correct this, but,
He was referring to a video someone posted showing a mountain in transit with the horizon, and as the top of the further mountain in transit with the horizon was well below the hieght of the observer it was pretty conclusive of the horizon being below the eye line. I noticed you ran away at that point.
I would suggest if you are going to quote someone else, you actually get the context, and quote correct.........
Here is the post in question (https://forum.tfes.org/index.php?topic=9492.msg152245#msg152245). Bobby remarks to it "If I'd seen that video earlier, I might never have bothered with this topic."
I assumed it was because the video and text provided calculation showing that the expected RET horizon dip was very slight, and because Bobby had been expecting something much more pronounced, but Bobby can speak on that.
I assumed it was because the video and text provided calculation showing that the expected RET horizon dip was very slight, and because Bobby had been expecting something much more pronounced, but Bobby can speak on that.
Here is the post in question (https://forum.tfes.org/index.php?topic=9492.msg152245#msg152245). Bobby remarks to it "If I'd seen that video earlier, I might never have bothered with this topic."
I assumed it was because the video and text provided calculation showing that the expected RET horizon dip was very slight, and because Bobby had been expecting something much more pronounced, but Bobby can speak on that.
My meaning was that that answers the question of whether or not the horizon is always at eye-level. I wouldn't have bothered with the question had I seen that. Not that the dip is "slight." But that there's no question of dip.
I'm still glad I got into it because I think it's always interesting to check for yourself and verify what others report. And though it does take some care, you it's within reach of anyone to detect.
The error of your reasoning is that you assume that you see the real horizon. Well, you see the 'horizon', but only as the limit of visibility of the sea surface. But not every limit of visibility of the sea surface is the real horizon, the geometric one, the one that matters in this case. Imagine that you live on flat land, let us assume that it is. And imagine that on the day you did this observation the surface of the sea was visible only at a distance of about 45.8 km. Well, with such assumptions, the result of your observation is the same as the one you showed. Is 46 km low visibility? Well, this is more or less average visibility. Most often the visibility reaches about several dozen kilometers. Only in exceptional circumstances, visibility, low above the surface of the sea reaches, for example, 200-300 km.
Why is visibility not infinite? There are a lot of reasons. The two most important are lighting (brightness) and air. What is air? Well, the air is fog. Yes, the air is 'diluted fog', because it differs from the fog only by the degree of dilution. In the air, as in the fog, various fine particles, dust and humidity are always suspended.
That is why we, the inhabitants of the earth, can not see infinitely, even if the earth is flat. Because there is air, or 'diluted fog'. I hope you understand that on a foggy day you also see a border of the sea surface and that this border does not coincide with the geometric horizon. Well, it is similar in every other day. But on a foggy day it is obvious to you, while on a normal day, as we can see it is not. On a foggy day the limit of visibility of the sea surface reaches, for example, half a mile, whereas on an average day, for example, 35 miles. Because the difference between the first and the second day is only in the degree of dilution of the fog.
But there is no day that you can see at an infinite distance !
The horizon of the sphere is at a specific distance depending on the height above the surface of the sphere. But the horizon of a sufficiently large flat surface ('infinite flat surface') is infinite. However, in the real world the limit of visibility of the sea surface is not the same as the geometric horizon. Because in the real world, apart from geometry, there are also physical phenomena, i.e. air, that is, 'diluted fog', which limits visibility.
Therefore, such observations with the horizon are not good for inferring the shape of the earth. Because most often we can not know if a boundary of the sea surface we see is a geometric horizon, or is it only due to the physical limitation of visibility. You would have to pump air out of the surface of the earth and the sea, so as to have a vacuum and then you would have a chance to see at any distance (of course with the right surface lighting!). But in ordinary conditions, the visibility, eg of the surface of the sea, is limited to several dozen kilometers.
In short:
1. One issue is the geometric horizon, and the second one is the horizon resulting from the limitation of visibility.
2. the geometric horizon over the infinitely large flat surface is level and does not decrease.
3. in the real world there are physical phenomena that limit visibility (e.g. air as 'diluted fog') => you can not see infinitely far away, even on flat ground => 'horizon' (different from the geometric one) always lowers below the level, even on a flat land.
So then if we can NEVER see a horizon, (because it is not at eye level, ever) how do people successfully calculate their position using the sun and stars at sea?
If there is not a clear horizon then we cannot take the altitude of the sun or stars to make our calculations.
Now if you know how how we do it, i would love to know what i have been doing wrong for the last 33 years.
Maybe you will enlighten me?
Well, here's some new information. Rowbotham's EnaG reasoning for the horizon coinciding with "eye level" is only for sea level range observations. And then only for periods when the horizon is subjectively "sharp." Else, the principle's applicability is less clear.
At altitudes near sea level where the earth's horizon is sharp, it may be at eye level per Earth Not a Globe's explanation of finite perspective lines. This has not been disproven.
We know that from an international flight the horizon is just a foggy mess.
At various other altitudes and atmospheric conditions, the situation is less clear; but you may keep trying. I can see in that video that it is not the clearest day.
Before I read those comments, I have to wonder why you think that should stymie my declaration of victory (if that's what I did). Critical comments rebutting things you think are decisive have never stopped you. Do you hold me to a different standard than to which you hold yourself?
Well, you were in error to quickly declare victory then. We can see that the matter was swarmed over in the comments section:
Well, you were in error to quickly declare victory then. We can see that the matter was swarmed over in the comments section:QuoteThe error of your reasoning is that...
So then if we can NEVER see a horizon, (because it is not at eye level, ever) how do people successfully calculate their position using the sun and stars at sea?
If there is not a clear horizon then we cannot take the altitude of the sun or stars to make our calculations.
Now if you know how how we do it, i would love to know what i have been doing wrong for the last 33 years.
Maybe you will enlighten me?
At altitudes near sea level where the earth's horizon is sharp, it may be at eye level per Earth Not a Globe's explanation of finite perspective lines. This has not been disproven.
We know that from an international flight the horizon is just a foggy mess.
At various other altitudes and atmospheric conditions, the situation is less clear; but you may keep trying. I can see in that video that it is not the clearest day.
I can see in that video that it is not the clearest day.It wasn't the clearest day today in San Diego either. But there was a horizon. Was it the "true" horizon? Allow me to walk you through this sighting of the Coronado Islands off of Mexico from San Diego's Point Loma.
https://books.google.co.uk/books?id=uQknbHhq2TAC&pg=PT308
Let a very small mirror (it need not be larger than a sixpence) be so suspended to a small support and so weighted that when left to itself it hangs with its face perfectly vertical—an arrangement which any competent optician will easily secure—and let a fine horizontal line or several horizontal lines be marked on the mirror; which, by the way, should be a metallic one, as its indications will then be altogether more trustworthy. This mirror can be put into the waistcoat pocket and conveniently carried to much greater height than the mirror used by Parallax. Now, at some considerable height—say five or six hundred feet above the sea-level, but a hundred or even fifty will suffice—look into this small mirror while facing the sea. The true horizon will then be seen to be visibly below the centre of the eye-pupil—visibly in this case because the horizontal line traced on the mirror can be made to coincide with the sea-horizon exactly, and will then be found not to coincide with the centre of the eye-pupil. Such an instrument could be readily made to show the distance of the sea-horizon, which at once determines the height of the observer above the sea-level. For this purpose all that would be necessary would be a means of placing the eye at some definite distance from the small mirror, and a fine vertical scale on the mirror to show the exact depression of the sea-horizon. For balloonists such an instrument would sometimes be useful, as showing the elevation independently of the barometer, whenever any portion of the sea-horizon was in view.
At altitudes near sea level where the earth's horizon is sharp, it may be at eye level per Earth Not a Globe's explanation of finite perspective lines. This has not been disproven.Can you point me to a clear explanation of what 'finite perspective lines' actually are. As I understand, the claim is that parallel lines can meet. But this is contradictory under the standard definition of 'parallel'. So the FE definition is different. What is the definition?
At altitudes near sea level where the earth's horizon is sharp, it may be at eye level per Earth Not a Globe's explanation of finite perspective lines. This has not been disproven.Well, you can't disprove it experimentally, to do so involves experiments over infinite distances which are a bit tricky...
We know that from an international flight the horizon is just a foggy mess.
At various other altitudes and atmospheric conditions, the situation is less clear; but you may keep trying. I can see in that video that it is not the clearest day.
Wouldn't concave refraction explain this? On the second stick man drawing with flat surface, suppose the light rays come down to touch the surface, then curve upwards gently to meet the eye. So it appears to stick man as though there is a visible horizon, whereas there really isn't.Possibly in some conditions. I originally drew that to demonstrate that even if the earth were flat the horizon would dip - the red line is supposed to indicate the limit of visibility.
However I am struggling to reconcile that idea with Tom's claims in another thread that mountain peaks really appear flat. I.e. if all the observations look as though the earth were round, even though it is really flat, why would Tom argue that the view of the mountains is consistent with flatness. One of these has to give.Tom often argues completely contradictory things depending on the circumstance, I find!
Try this for size.Wouldn't concave refraction explain this? On the second stick man drawing with flat surface, suppose the light rays come down to touch the surface, then curve upwards gently to meet the eye. So it appears to stick man as though there is a visible horizon, whereas there really isn't.
I believe that under the Electromagnetic Accelerator theory, in which light is universally bending upwards, the effect would have a side effect of the sun shining its same face over the entirety of the earth's surface. Extreme angles of the sun would be bent away from the observer and never seen.Of course on the real earth light from the sun is usually bent down slightly, typically shout 0.6° at the horizon.
(http://i34.tinypic.com/219xuo4.gif)
Possibly in some conditions. I originally drew that to demonstrate that even if the earth were flat the horizon would dip - the red line is supposed to indicate the limit of visibility.That's an essential for belief in a flat earth, it's not problem for some.QuoteHowever I am struggling to reconcile that idea with Tom's claims in another thread that mountain peaks really appear flat. I.e. if all the observations look as though the earth were round, even though it is really flat, why would Tom argue that the view of the mountains is consistent with flatness. One of these has to give.Tom often argues completely contradictory things depending on the circumstance, I find!
At altitudes near sea level where the earth's horizon is sharp, it may be at eye level per Earth Not a Globe's explanation of finite perspective lines. This has not been disproven.
We know that from an international flight the horizon is just a foggy mess.
At various other altitudes and atmospheric conditions, the situation is less clear; but you may keep trying. I can see in that video that it is not the clearest day.
Wouldn't concave refraction explain this? On the second stick man drawing with flat surface, suppose the light rays come down to touch the surface, then curve upwards gently to meet the eye. So it appears to stick man as though there is a visible horizon, whereas there really isn't.
However I am struggling to reconcile that idea with Tom's claims in another thread that mountain peaks really appear flat. I.e. if all the observations look as though the earth were round, even though it is really flat, why would Tom argue that the view of the mountains is consistent with flatness. One of these has to give.
At altitudes near sea level where the earth's horizon is sharp, it may be at eye level per Earth Not a Globe's explanation of finite perspective lines. This has not been disproven.
We know that from an international flight the horizon is just a foggy mess.
At various other altitudes and atmospheric conditions, the situation is less clear; but you may keep trying. I can see in that video that it is not the clearest day.
These were taken at the same location (380' above sea level), viewing the Middle Islands of Islas de Coronado, about 20 miles away:
(https://1.bp.blogspot.com/-qSDMu1slAUE/WwXKvsQCk0I/AAAAAAAAJxg/_0JGxASXM7YWLeCuN-vp1twszVWdZHG6wCLcBGAs/s1600/Coronado%2BHorizon%2B3.jpg)
Yesterday evening was much clearer, but still hazy enough to maybe not qualify as a "sharp" horizon.
Today, the marine layer haze is thicker and definitely not a good horizon viewing day (currently).
Comparing the two images: in the sharper of the two you can more clearly make out a horizon line slightly higher than in the later, hazier one.
I can tell in the clearer one that the sea plane rises more behind the islands. I can't tell that in the hazier one, where the plane of the sea appears to end near the islands themselves.
The challenge/question is how clear is clear enough? At what point can we confidently say there will be no more rise in the horizon line with additional clarity? I know where that is in globe earth. But if I don't want to bias this with a globe earth premise, what is the flat earth criteria for knowing you are looking at a 'true" horizon?
For reference, the larger island on the left has summits near 400'. (Wikipedia is wrong, listing both islands as rising to only 100', which is true for the small one on the right but obviously not true for the one on the left.) Since my height was 380' (+/- 5') the summit of the large island is right about "eye level" in the picture. Will I only be seeing the "true horizon" if it matches with that summit? If so, then I don't think I've ever seen a "true" horizon.
Doesn't this lend credence to the idea that the state of the atmosphere in the distance can move the horizon down?Yes. That's why I posted these. Atmospheric surface haze will push the apparent horizon "down" (aka closer).
Doesn't this lend credence to the idea that the state of the atmosphere in the distance can move the horizon down?Yes. That's why I posted these. Atmospheric surface haze will push the apparent horizon "down" (aka closer).
But what about "up"? What's the "up" limit? (aka further).
How do you -- and I mean, you, Tom Bishop -- know if it's clear enough to make an "eye level" evaluation?
1. Rowbotham discusses Theodolite Tangent here: http://www.sacred-texts.com/earth/za/za45.htm
6. Bobby personally performed this sort of water experiment himself and can tell you how sensitive and complex this seemingly simple experiment is. He decided to abandon it. Read his thread: https://forum.tfes.org/index.php?topic=9492.0
1. Rowbotham is only useful as an example of how to bamboozle simple folk with mindgames and twisted logic.
6. The water level equpiment is more than accurate enough for purpose.
Bobby's thread chronicles his journey and the issues faced. It is not a simple experiment.
Surveying is not easy. It is incredibly difficult and sensitive.
Surveying is always in error. Always. The device needs to be finely aligned, positioned, and calibrated. Even then, there is still inherent error.
http://whistleralley.com/surveying/theoerror/QuoteAs any surveyor should understand, all measurements are in error. We try to minimize error and calculate reasonable tolerances, but error will always be there. Not occasionally; not frequently; always. In the interest of more accurate measurements, we look for better instruments and better procedures.
The greater the distance you are trying to align your devices with, the greater the potential error. All devices need to be of superior calibration.
...
One major design improvement came with the invention of the transiting theodolite. With this innovation, the telescope was able to swing all the way over on the trunnion axis. This in itself did not reduce any of the inherent error in the instrument, but it gave surveyors the means of doing so. When the scope is inverted, the instrument error is still there, but most of the error reverses direction. By taking the mean of an even number of observations, half direct and half inverted, the error is turned against itself and greatly reduced.
The theodolite actually has one advantage over most levels. By inverting the telescope, the collimation can be checked from a single setup.
A few seconds, or even minutes, of error here makes no appreciable difference in horizontal distances, but it can play all havoc with elevations. Unlike the horizontal angle errors, this one is constant, which is to say, it is not affected by changes in the direction of the sight. That makes it a fairly simple matter to correct the angle without even adjusting the instrument. In fact, electronic instruments typically have an onboard routine that will measure and correct the vertical angle error. Push a few buttons, sight a target in both positions, and have the instrument store the correction. The procedure takes only a couple of minutes, so it can be done at the beginning of each work day.