What is this

[macca2]

This is something my son picked up at an auction and asked Dad what is it.
I have no idea.
He says it is about the size of a CD
Can someone help.

Thanks Macca

[macca2]

A pic might help

[craigb]

Buggered if I know.

It's beautifully made though. Some sort of scientific instrument I'd say.

[Ivan in Oz]

Looks Nautical
Does it open up at all?

[Auld Bassoon]

Hmm, bit of a challenge there..

It seems to have an aperture (at the bottom of the pic) that looks as if it might be a receptacle for a measuring?) arm. As well, there are two square keys (near the top right of centre) that seem to suggest a clockwork mechanism.

The scale has a magnifying optical attachment - but I'm confused by the (regulating?) arms...

Is the brass cylindrical piece to the left of the pic a receptacle for the main mechanism shown? If so, this would suggest some transportability.

Very curious to know what you find out!

[Skew ChiDAMN!!]

Is that a gimbal mount on the front side of the thingy? What range does the scale cover?

What really has me wondering is: why two clockwork winders? Assuming 'tis clockwork and not just similar looking adjustment mechanisms.

[AlexS]

I'll have to go to one of my old textbooks to find the correct name, but I believe it's a survey instrument used for marking right angles off a survey line. Never used one, but I think you look through the eyepiece and see a split image through the two lenses. More tomorrow.

[macca2]

I have not seen this thing myself but I am told there are two mirors inside and when you look thru it and move the arms it does seem to measure angles.

[Ivan in Oz]

I can not see the reflection of the Second arm under the one with the Lense.
Like to see Photograph from other angle.
There is what liiks like an eye hole at the Bottom front of the body...........
But you all realised that.

[AlexS]

OK, it's called an optical square.

description from the textbook."a small box containing prisms or mirrors, so arranged that when the square is held to the eye and a point on a line is sighted through it, a sight is also obtained along a line at right angles to it.

There's also a diagram that I'll photograph & post if I can, tomorrow.

I believe the "winders" are for making small adjustments to the mirrors inside, and the lense on top is for reading the scale below. Is it a vernier scale?

[Hard Wood Stud]

Hi,
It looks to me like a very old Chalk Line Reel??? Or perhaps even some sort of a timming case housing???
Cheers
Hard Wood Stud

[DanM]

I reckon it measures distance!

[craigb]

OK, it's called an optical square.

description from the textbook."a small box containing prisms or mirrors, so arranged that when the square is held to the eye and a point on a line is sighted through it, a sight is also obtained along a line at right angles to it.

There's also a diagram that I'll photograph & post if I can, tomorrow.

I believe the "winders" are for making small adjustments to the mirrors inside, and the lense on top is for reading the scale below. Is it a vernier scale?

Looks like a wonderfull example of the Instrument Maker's craft.

Sure it's been superseeded by lazers and what not but it still amazes me that such a precision tool was esentially hand made.

I'm in awe of the maker's skill.

[ptc]

Send pics to the collectors on abc tv.

[macca2]

Thanks for all the replies. Alexs...you are spot on, I did a Google search on Optical square and there it was.
Also known as a pocket sextant and have been around for 100 years and are still available today although nothing like the photo I posted.
They range from a few dollars to a couple of handred dollars on the second hand market, but I have no idea how you tell a good one from a bad one.
Made in Germany, England and the USA and probably elseware.
Been an interest exercise and thanks again
Macca