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Historic Aviation => People and Units => Topic started by: RvanTonder on March 25, 2011, 09:28:22 AM

Title: Compass P8M information needed
Post by: RvanTonder on March 25, 2011, 09:28:22 AM
Good Day Everyone

I have a Type P8M compass inhereted from my late grandfather. For some reason I cannot attach my pictures into this forum. I must be honest, I do not know much about the compass, but would appreciate someone out there to give me some information.
Some details: Type P8M
Have all the liquid inside still.
Stamped in the box Examined August 1943
Air Ministry No: 6A/726
NO: 141 240B

I have read some information regarding the production etc, but I gave no clue what the value of this is, which plain it would have been used in, where it comes from etc. There is a AFT printed in white on the brim of the compass.

Any help will be appreciated.

Title: Re: Compass P8M information needed
Post by: Edgar Brooks on March 27, 2011, 09:12:39 AM
"P" compasses were used in every British aircraft, and are still around (in fact, one company, SIRS, in Kent, still manufacture them.) The "M" suffix usually means "modified," and I hope that it means that the powder in inner glass tubes, and the paint on the cardinal points and the wires under the glass, has been replaced by material that reacts to u/v light, rather than glowing, itself, in the dark. I suggest that you get it checked, first to see if it does glow, then try it under a u/v lamp.
 When first made, the compasses had tubes of radium powder attached to the "spider" inside the bowl, and some areas, like the cross-wires in the lid, had radium paint on them. To the unknowing (and that includes an awful lot of museum staff) the word "radium" brings a sharp intake of breath, and an often almost hysterical reaction. However, if the glass is undamaged, the radiation risk is minimal (one check is to look at the paint, itself; if it's gone brown, with black specks, it's a fair bet that it's radium,) but on no account should the lid be removed, since old radium paint turns to dust, and, if you breathe it in.....................
 If the paint, and the inner tubes don't glow in the dark, you're fairly safe to assume that it's been modified, but a geiger counter would still be advisable; I've seen compasses where the tubes have been replaced, but the paint on the wires left "as is."
As to value, I don't have a clue, but they certainly aren't rare.

Title: Re: Compass P8M information needed
Post by: Jaybee on March 28, 2011, 03:51:02 PM
A link which may be of interest and use to Rvan and any others interested in WW2 aircraft instruments