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General => The Common Room => Topic started by: AntoR22 on Saturday 01 June 13 12:21 BST (UK)
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Hi All..
Didnt quite know where to post this so here might be a good start...
Does anybody out there know anything about old brass compasses ?? . One has recently come into my possession . I'll attach some photo's of it which might help identification there's no manufacturer's name on it just an anchor crest So far I'v reckoned that its either French, Spanish, Portugeese, or Italian because there is an O instead of a W for the west direction and thats as far as I'v got..
Have Fun...
Anthony.
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What a lovely item.
Seems it is a Mariners Pocket Compass.
One website had the following
The names of the cardinal and ordinal directions are derived from the English language but their initials, N, S, E, and W are internationally known. The Open Face Mariner's Compass substitutes the West point with an O, an abbreviation for the Latin term Occidens, to fall or set, as in the sun.
Susan
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Hi Susan..
I think its a lovely little keepsake too . Would you have any idea of age or origin ??
My thinking for the O was a word like Ouest which I thought translated to west .. but yours a much more sensible reason ..
Thanking you ... Anthony
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Only a guess but I reckon around mid to late 1800's
Hopefully an expert will come along to help
It's certainly a beaut.
Susan
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Good afternoon,
It's a shame it has lost it's needle which would have lain across the bezel in the centre. It is unusual in only having 8 cardinal points marked instead of 16. Instead it is marked every 5 deg and numbered every 30. It also has magnetic north marked by the thin arrow to the left of the N. Lining up the needle with this arrow would have shown true north in line with the N.
It shows a magnetic variation of 15 deg so if you know the annual change in the variation for the past couple of hundred years you should be able to date it quite accurately. For a british compass it would normally be in agreement with the 0 meridian and it's variation. However, older compasses may have been made in line with the local meridian and variation which can vary by several minutes from one side of Britain to the other.
John915
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A word of warning, be careful when buying this type of compass as antique, there are a lot of copies and replicas about, some better than others and some dealers try to pass them off as antique. Have a look here; http://www.brasscompass.com/
and; http://www.handcraftednauticaldecor.com/pocket-compasses-brass-nautical.php
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Hi all and thanks for the replies very informative ..
John I'm wondering if it ever had a needle ??? the whole dial rotates .. I noticed the arrow and guessed what it was for and what you say about variations makes sense but where would I get the figures to do the math on it .
It could be just a copy as it has no numbers or names on it ..
Thanking All .... Anthony
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Hi Anthony,
Have a read here (Link to website is http://www.stanleylondon.com/opencompyellow.htm (http://www.stanleylondon.com/opencompyellow.htm) Picture there looks same as your one)
Determining your Position with a Dial Pocket Compass and a Map
by Eric Newman
So you've used a standard pocket compass with a compass needle to take a sight and it was a bit of a pain. Now you are wondering if there is an easier way. Yes, a pocket compass with a floating compass dial makes sighting much easier.
To take a bearing you need a protractor, which is a circle divided 0 - 360 degrees, and you have to reference the protractor to north. Luckily, a protractor is actually built into the compass rose. When using a compass with a compass needle, you need to orient the compass rose to north, which you do by rotating the compass rose until the north end of the compass is exactly over north on the compass rose. That is a bit of a pain.
In this tutorial we will use an open face compass with a floating compass dial marked 0 - 360 degrees. See Figure 1. The beauty of a compass with a floating compass dial is that the compass magnets are built into the floating compass dial, so it automatically aligns to north, and you do not have to align it manually.
To locate your position, first locate two or three landmarks that you can also locate on your map. A landmark can be a water tank, church spire, radio antenna, or a distant hilltop. Ideally, you want two landmarks about 90 degrees apart, or three landmarks about 120 degrees apart. You do not want any two landmarks to be in a nearly identical heading, or 180 degrees apart. It is also critical that you can clearly see the landmarks and locate them on your map.
Now find the magnetic bearing for the first landmark. Face the direction of the landmark and hold your floating compass dial pocket compass just below eye level. Make sure you hold the compass steady and level. Sight the landmark across the center of the compass bearing and read the degree marking on the compass dial directly away from you. Note this heading because you will need it to find your location on your map. In Figure 2, we are sighting a bearing of 222 degrees.
Repeat this procedure with the next landmark and note this second angle. For our example, the second landmark is in the direction of 186 degrees. If you can identify a third landmark and determine its magnetic bearing, that is even better. Figure 1 - Compass with a Floating Compass Dial
Figure 1
Click for larger image
Figure 2 - Taking a Sighting of 222 Degrees Using the Floating Compass Dial
Figure 2
Click for larger image
Now transfer your landmark headings directly onto your map. Lay your map out flat and locate the compass rose on the map. Sometimes there are two concentric compass roses, with one in a slightly different orientation from the other. If this is the case, use the one marked "magnetic."
You can either transfer a parallel line between your landmark and the map's compass rose, or you can place your pocket compass directly onto the map and transfer the landmark heading to the map's compass rose by moving the compass. With the compass aligned to the map, you can use its compass rose to draw a line through the first landmark using the angle of the first landmark's bearing. Repeat this with your other landmarks, drawing a line for each in the direction of its direction.
If you do not have a compass rose on your map, then north is up, east to the right is 90 degrees, south is 180, and west is 270 degrees. The problem is that these are probably referenced to true north, and your pocket watch style compass reads magnetic north. The difference between true north and magnetic north is the local magnetic declination, which depends on your general area. You need to determine the declination in your area. The magnetic declination in Los Angeles is 13 degrees east. New York City is 13 degrees west. If you are lucky enough to be lost just west of the Mississippi River on the agonic line where the declination is zero, then magnetic north and true north are the same, so your compass reads true north. If you are not so lucky, simply adjust your compass readings for your declination. For New York where the declination is 13 degrees west, just subtract 13 degrees to your compass reading to get a heading referenced to true north. In the Los Angeles area with 13 degrees east declination, add 13 degrees to your compass reading. And get a better map.
Refer to the topographic map in Figure 3 and note the 222 and 186 degree lines. Where the two lines intersect is your location. If you have three landmarks, consider your position to be in the triangle formed by the three lines. The triangle should be fairly small. If your triangle is large something is wrong. You probably incorrectly identified a landmark, misread the heading, or did not draw the lines correctly. This is a good reason to use three landmarks, as two lines from two landmarks will not show a problem. The more landmarks you use, the more confidence you will have in your position. Figure 3 - Topo Map with sighting lines
Figure 3
Click for larger image
Now that you have your location, verify that it is reasonable. Using the example in Figure 3, you should be near a reservoir and near the top of a ridge. The ridge near you should be running roughly east-west and the closest shore of the reservoir should be southwest of you.
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Hi Susan
Yes it does look identical to that one I wonder is there a way of telling a real one from the reproduction one .. he only difference i can see is mine a bit worn and has anchor on back
Thanking You ... Anthony
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Yours certainly looks old and (excuse this) dated in comparison to the replicas which seem to have silver metal casings. Is it on the heavy side? I only ask as if it is true brass it may be heavier than a "brass metal" lookalike (and I suspect the glass will be thicker.) Then again there are some clever people who are able to replicate objects to look and feel just like an original, Darn.. ???
Oh, I do wish an expert could tell us.
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Hi Susan
As it happens theres a gram scales in the house .. God knows why ??
Mine weighs 69.5 grams and ad for reproduction says its 65 so mine fraction heavier ?
Glass looks pretty thick the biggest difference i think is the back even not counting the crest the reproduction looks like one flat piece metal where mine has a sorta insert centre to it ??..
Anthony
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Oh yes. I see what you mean. And the weight (I would think) is a giveaway.
I wonder if you could find a forum for mariners compass' - then post a picture.
Worth a go.
Susan
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Most of the replicas are made of brass, it is not a precious metal, although fairly expensive. Some I have seen have phillips head screws, that a dead give away.I would also have expected the box to have jointed corners, most likely dovetail joints. The modern ones tend to have mitred corners. It may not be the original box.
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Good evening,
You are correct Anthony, it didn't have a needle as it's a floating dial. Susan's link brings up a good point, the one near the end which is practically identical to yours. The description says the small arrow points to true north and the N to Magnetic north. This gives it a positive variation ie; to the east of true north.
In england we have a negative variation, as at May 2013, 1 deg 38 mins west in London. So the compass was not for use in this part of the world, but probably the Pacific coast of the USA. Or that ocean at least, the variation in the US goes from roughly 13 deg west on the east coast to 13 deg east on the west coast.
I have searched online for a table of variations over the years but no luck.
John915
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Hi John .. Thanks for that information it looks as though this compass has seen a bit of the world and it seems a science of its own working out variations ..
It could be a copy but it feels old,,,, hard to explain that... There is no screws on it anywhere the ring at the top screws in , I'm not quite sure how it was put together maybe inset at back screws in ?? or glass was put in last ??
I suspected box was not original its got mitred joints and too good a condition...
Many Thanks Anthony
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Hi All..
....no manufacturer's name on it just an anchor crest So far I'v reckoned that its either French, Spanish, Portugeese, or Italian ...
The "fouled anchor" symbol would certainly suggest the British navy.