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Pooh-Bah
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Pooh-Bah
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Looking through some old books last night I came across A Dictionary of Civil Engineering published by Penguin in 1958. Some good words in there, but most probably of little interest to most people. One entry caught my attention:
Agonic line – a line on a map of the earth along which the magnetic declination is zero. From the Greek; agonios, without angle.
To find this line I guess you draw a line between the magnetic North Pole and the geographic North Pole and then project that line both ways around the globe. The idea is new to me and I cannot see that it has any use, although the dictionary says that it is a surveying term. I’ve done my share of surveying for roads and railways in years past, but not once did I think ‘Damn, I wish I knew where the line of zero declination was’. Does anyone know how surveyors use it, or why they might need to know it?
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Carpal Tunnel
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Carpal Tunnel
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Dear dxb: If you have done surveying you know more about it than the rest of us, I should think.
I know that the compass points to magnetic north, and a correction has to be made to get
true north, but I don't know how surveyors handle that critically important task. It will give me
something to look up, though I expect a headache.
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Carpal Tunnel
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Carpal Tunnel
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draw a line between the magnetic North Pole and the geographic North Pole
Due to local variations in the magnetic field it isn't quite that easy. One could google something and come up with specifics.
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Carpal Tunnel
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Here is a URL that explains it, but I ;haven't read it yet, and expect difficulty making useful post about it. http://www.geoshare.org/new_web_site/technical/12/html/1.htmP.S. Two hours later, I went back and tried to understand that URL site. As I feared my smarts have deteriorated to point I cannot master it. My respects to those of you who can.
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Carpal Tunnel
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Carpal Tunnel
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Here's a link to a computer generated model of the Earth's magnetic field. Note most of the spaghetti is probably in the core, but it gives you an idea. http://antwrp.gsfc.nasa.gov/apod/ap021125.html
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Pooh-Bah
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Pooh-Bah
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Gentlemen,
Thank you for those links. The model of the magnetic field shows amazing complexity - it resembles the head of a rather tatty corn dolly. I was aware that the strength and direction of the field varies with time and place and the Geoshare site confirms that. In fact what that site says leads me to doubt whether an agonic line, other than a very short local one, could in fact be drawn. Perhaps the technology has developed since the space age and a more simplistic approach was taken in the '50s. I guess that it is of more significance in mapping, for example, than in surveying for the construction industry. Because the link is to a Geoshare site the information one can reach from it is connected to the oil industry. I'll look wider.
Thanks again. dxb.
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Pooh-Bah
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I've just consulted Mrs Rhuby, who was a cartographic draughtsperson for many years, but she disclaims any knowledge of the term at all. Not that this proves anything, other than that it was not a term in common use amongst cartographers up to around 20 years ago. (Indeed, when asked the meaning of the word, she suggested that it described the tenor of letters written to the advice columns of women's magazines!) 
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Pooh-Bah
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Nice one - what's her take on alidade?
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Carpal Tunnel
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alidade
Isn't that a city in Australia?
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Carpal Tunnel
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agonic advice columns... yes, derived from "Agony Aunts" (the originals of whom are both gone from our papers now.)
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Carpal Tunnel
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Dear Faldage: This must be one of your dyslexic days. Here is rather good URL about true north vs magnetic north: http://makeashorterlink.com/?Q23F428B2
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Carpal Tunnel
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Carpal Tunnel
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Sweeney agonistes and tsuwm (aka ron obvious) obviousizes.
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Pooh-Bah
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what's her take on alidade?
C'mon dxb - she ain't that old! When did you last hear of an alidade being used (unless the name has been nicked to apply to the thingy you squint through on modern, electronic devices!)
They were certainly in use in the C19, and probably well in C20, but I think they were out of favour by the 1950s, at latest.
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Carpal Tunnel
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out of favour by the 1950s
I used one in the early '60s.
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Pooh-Bah
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Ah! - but what did you use it for ???
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Carpal Tunnel
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Carpal Tunnel
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Dear RC: Faldaage used the alidade to learn the direction to Adelaide.
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Pooh-Bah
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Of course, Bill - how silly of me!
(Sure he wasn't looking for Sweet Adeline?)
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Carpal Tunnel
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>tsuwm obviousizes.
yes, and it turns out to have been a futile attempt to elicit a response, wherein I could reply, "they were the founding sisters of the agonic advisory." well, nearly futile, as there is your response, and you're not exactly birdseed, ASp.
-ron obvious
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Pooh-Bah
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When did you last hear of an alidade being used (unless the name has been nicked to apply to the thingy you squint through on modern, electronic devices!)
You're quite right Rhuby, I don't think it is in use now, but like Faldage I certainly used one in the '60s and according to this 'ere dictionary "In USA the term is also applied to the telescope and its attachments on a theodolite...". So there we are then. Mind you, I did say the dictionary dated from 1958. Some of the stuff in it is downright quaint.
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Carpal Tunnel
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... downright quaint.
Clearly, the most arcked level of quaint.
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Pooh-Bah
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Another word from the Civil Engineering dictionary:
Chemise: a wall which revets an earth bank; i.e.: a wall that protects an earth bank against weathering, without acting to retain or strengthen.
We usually think of a chemise as a shirt or blouse. The American Heritage Dictionary gives its source as Central Semitic, to enclose, and presumably that is the connection with the wall.
“Chemise from Late Greek kamision, probably from a Semitic source akin to Ugaritic qm , a garment, Arabic qam , shirt, both akin to Hebrew q ma , to enclose with the hand, grasp.”
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Carpal Tunnel
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Day-um! I should know a straight-man set-up when I see one. My agonic apopligies*, tsuwm. ______ *I, like RhubarbCommando, know when to leave a good typo alone. 
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Carpal Tunnel
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Carpal Tunnel
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I am so like totally not going there.
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Pooh-Bah
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Could be the origin of those books - you know - bodice rippers?
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Pooh-Bah
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I, like RhubarbCommando, ... and I, I like you, to, AnnaS 
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Carpal Tunnel
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Dear RC You'd like her to what?
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Carpal Tunnel
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Pooh-Bah
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Bill, I'd like her to much! and your comment is baah-ed, AnnaS! 
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Carpal Tunnel
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Well, we've certainly gone astray from Magnetic North!
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Carpal Tunnel
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formerly known as etaoin...
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Carpal Tunnel
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Damned compasses can fool some smart people. I remember deer hunting with a friend who
had a very elaborate compass. It was after dark, so we were just planning to do next morning
He looked into eyepiece of the compass, and said "that's North". and pointed - South. The Pole Star
was behind him. He had not thought to look for it.
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Carpal Tunnel
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...said "that's North". and pointed - South. The Pole Star
was behind him. He had not thought to look for it.
Well, if he had gone off in that direction he would have been quite correct (provided that he went about eighteen thousand miles)!
It's not hard to read the wrong end of a compass needle. Pity they can't make only half of a bar magnet - the North end - to avoid all that confusion. You know: just cut off the South part! [straight-face-e]
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Carpal Tunnel
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alidade
Isn't that a city in Australia?
No it's a future headline in Variety after the passing of Ali McGraw.
TEd
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Carpal Tunnel
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My uncle Tate Remington did exactly that, and sold compasses that always pointed the wrong way. Certainly, "He who has a Tate's is lost."
TEd
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Carpal Tunnel
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gone astray
Whilst singing the piece recently it occurred to me the imagery of the piece, that sheep are all off doing their own thangs, is not the one we customarily ascribe to sheep, that of following the herd, doing what everyone else is doing. Anybody know which of these stereotypes is more sheeplike IRL?
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Carpal Tunnel
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sheep are very cleaver...
formerly known as etaoin...
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Carpal Tunnel
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very cleaver
Is that cleofan cleaver or cleofian cleaver?
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I think I can safely say, yes.
formerly known as etaoin...
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