Help with an unusual compass

Pitlamp

Pitlamp

Well-known member
My neighbour just asked me if I knew how an unusual compass works. It belonged to her husband who has sadly passed away and she'd like to be able to use it. We think it allows you to determine your latitude, using the sundial ring and the curved arm (both of which are on hinges).

Can anybody help? Even if you just know the correct name for such a device, which would give a google search term, at least.

Compass(1).jpeg
 
Winnat's Caver

Winnat's Caver

Member
I'm reminded of a compass trick we learnt at scouts, where you could use the position of the hour hand on a watch to tell which way was north. Perhaps the sundial serves a similar purpose here?
 
F

Fjell

Well-known member
It is a sundial (clock). The round bit hinges up using the curved bit to hold it so it becomes perpendicular to the sun. You use the compass to align it. You could use it to roughly find solar noon.

If you know the height of noon you can in principle find latitude, but this thing would put you somewhere between the Scillies and Orkney on a good day. You need to measure it to within a minute of arc to be within a mile, I have just about managed it tested against a GPS, always fun when you are going up and down a lot.
 
Bob Mehew

Bob Mehew

Well-known member
Do remember after next Saturday to correct for BST if you use 12 noon to postion north by the sun. Though of course being a bit westward of Prime Meridian you will need to either take account of the minutes and seconds, or work out what it is from the compass.
 
F

Fjell

Well-known member
I have yet to notice anyone rotate a sundial back and forth for BST, but I’m sure that person is out there.

Noon is currently 12.15 in Kendal. BST really messes that up.
 
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