And here is a photo that I didn't post, it's a close-up of one of the bone
pieces:

http://img.photobucket.com/albums/v8...pic2561nda.jpg

Tell us more about the slits with the bone. Is it one big groove all the
way around...sort of like a spool, with bone disks jammed in (and how much
space is between the central hub and the bones? Or is this more like two
separate pieces joined by several bone axles. And are all the bone pieces
inset the same distance? Might this be something that had a rope twisted
around it and that turned like a top when the rope was pulled? Or I'm
starting to think about a counterweight for a bell pull, but I'm not sure
of the role of the bones and slit.

Here is the owner's reply to your questions:

The slit is 3/8" wide and 1" deep, with 1/4" pieces of bone. Yes, it is
like a spool with the bone pieces wedged in. The bone is flush with the
outer edge (except for one that has slipped into the slit) and I believe
they are equidistant from each other. I could see it being a
counterweight... Although the bottom is not 'finished'.

On 5/26/12 3:11 PM, Rob H. wrote:

And here is a photo that I didn't post, it's a close-up of one of the
bone
pieces:

http://img.photobucket.com/albums/v8...pic2561nda.jpg

Tell us more about the slits with the bone. Is it one big groove all
the way around...sort of like a spool, with bone disks jammed in (and
how much space is between the central hub and the bones? Or is this
more like two separate pieces joined by several bone axles. And are
all the bone pieces inset the same distance? Might this be something
that had a rope twisted around it and that turned like a top when the
rope was pulled? Or I'm starting to think about a counterweight for a
bell pull, but I'm not sure of the role of the bones and slit.

Here is the owner's reply to your questions:

The slit is 3/8" wide and 1" deep, with 1/4" pieces of bone. Yes, it is
like a spool with the bone pieces wedged in. The bone is flush with the
outer edge (except for one that has slipped into the slit) and I believe
they are equidistant from each other. I could see it being a
counterweight... Although the bottom is not 'finished'.

If it's for sighting sunups and sundowns, I can see how the slit would
be necessary.

Normally, the moments of sunrise and sunset are when the tip is visible
on the horizon. Mathematically, you want the moment that the center is
on the horizon. Due to refraction, when the tip is visible, the sun is
actually 0.75 degrees below astronomical sunup or sundown. The ancients
would have realized the problem when summers were 2 to 4 days longer
than winters. A one-day error could throw the Jewish calendar off by a
month.

The slit would let you see the sun when it was optically at the correct
distance above the horizon. When tiny head movements caused it to wink
on both sides of the core, you would be at the correct azimuth.

Ninety percent of American men have an interpupillary distance between
55 and 70mm. If the user had an IP of 62mm and the core of the mystery
item is 86mm, he would stand 250cm (about 9 feet) away to have the core
just block the sun. At that distance, the slit would be 0.2 degree
high. The center of the slit should be 22mm above the observer's eye level.

Sunlight would be visible in the slit about 4 minutes. When the
observer first saw a glint of light, it would be his 2-minute warning.

Just above eye level and 86cm in front of the observer should be a rod
to suspend a plumb bob on a loop. At that distance a degree would be
29mm. The reason for the 86cm distance in front of the observer is that
at that distance, when the string lines up, it will appear tangent to
one side of the ball and then the other as the observer closes one eye
and then the other.

The slit ball design could be thousands of years old, but steel eye
screw makes me think this item was made after published equinox dates
were available anywhere on earth, regardless of the local civil calendar.

In WWII, the British and the Germans had sun-sighting devices to
calibrate compasses on aircraft on the runway. The ancient Vikings set
their compasses that way. The wooden ball looks more precise than would
be needed to calibrate a compass. I wonder if it was for map making.

In Washington's time, surveys were likely to be very poor because
compass readings aren't reliable. Yet accurate maps were drawn long
before Washington. With a slit ball, an explorer wouldn't even have to
know the time or date to determine north within a fraction of a degree.
Then he could get precise bearings with a transit.

It would take four markers, like the bone spacers. The first would go
below the ball. The second would mark the spot from which sundown was
sighted. The third would mark the spot from which sunrise was sighted.
The transit would then be placed over the first marker. It would
bisect the angle between the other two markers in order to place the
fourth marker due north.

If the map maker wedged the spacers in the slit and wrapped the ball
tightly, the ball and spacers should travel well.

I just don't know where to find a picture of a map maker using a split ball!

On 5/26/12 3:11 PM, Rob H. wrote:

And here is a photo that I didn't post, it's a close-up of one of the
bone
pieces:

http://img.photobucket.com/albums/v8...pic2561nda.jpg

Tell us more about the slits with the bone. Is it one big groove all
the way around...sort of like a spool, with bone disks jammed in (and
how much space is between the central hub and the bones? Or is this
more like two separate pieces joined by several bone axles. And are
all the bone pieces inset the same distance? Might this be something
that had a rope twisted around it and that turned like a top when the
rope was pulled? Or I'm starting to think about a counterweight for a
bell pull, but I'm not sure of the role of the bones and slit.

Here is the owner's reply to your questions:

The slit is 3/8" wide and 1" deep, with 1/4" pieces of bone. Yes, it is
like a spool with the bone pieces wedged in. The bone is flush with the
outer edge (except for one that has slipped into the slit) and I believe
they are equidistant from each other. I could see it being a
counterweight... Although the bottom is not 'finished'.

I haven't found documentation about sighting the sun to survey prior to
1836, but this article says the solar compass was a marvel of the 19th
Century. As of 1973, the Bureau of Land Management still recommended it.

http://en.wikipedia.org/wiki/Solar_compass

The surveyor had to know the latitude, look up the sun's declination,
and know the local time. The solar compass would allow him to get
bearings at several sites during the day.

If he knew his latitude and the date and had a table of sunup/sundown
azimuths, he could use a sighting device such as a split ball to make an
equally precise determination of north, but he would have to do it at
sunup or sundown. Perhaps a surveyor who didn't often need to determine
true north would have done it this way in the 20th Century, rather than
buy an expensive instrument for occasional use.

If the mystery item was invented to sight the sun, perhaps the hole in
the bottom was for a plug from which a plumb bob hung.

I haven't found documentation about sighting the sun to survey prior to
1836, but this article says the solar compass was a marvel of the 19th
Century. As of 1973, the Bureau of Land Management still recommended it.

http://en.wikipedia.org/wiki/Solar_compass

The surveyor had to know the latitude, look up the sun's declination, and
know the local time. The solar compass would allow him to get bearings at
several sites during the day.

If he knew his latitude and the date and had a table of sunup/sundown
azimuths, he could use a sighting device such as a split ball to make an
equally precise determination of north, but he would have to do it at
sunup or sundown. Perhaps a surveyor who didn't often need to determine
true north would have done it this way in the 20th Century, rather than
buy an expensive instrument for occasional use.

If the mystery item was invented to sight the sun, perhaps the hole in the
bottom was for a plug from which a plumb bob hung.

The owner had said that a couple people had suggested that the wooden item
was originally mounted on a staff at the hole in the bottom and that the top
metal piece was added at a later date. Your compass theory sounds
plausible, hopefully we'll get an answer for it one way or the other but if
I had to bet I'd say it will remain unidentified for a while.