compass

[scall38]

Hi all. Really interested to hear members opinion of this compass. It came with a pocket watch which I will post later thanks.

[johnboy]

Is there a WD or broad arrow marking?

[IPT]

Described on this sale site as a bearing compass, used to verify the course of a vessel.

http://www.antik.it/Antique-compasses/4232A-Nautical-compass/

Edit - Having said that, it's described elsewhere as a WWI VERNER'S PATTERN VIII BRASS MILITARY COMPASS

[scall38]

Thanks . I will check for the markings later. Here is another image for now.

[IPT]

WWI VERNER'S PATTERN VIII BRASS MILITARY COMPASS

http://www.the-saleroom.com/en-gb/auction-catalogues/mulberry-bank-auctions/catalogue-id-srmul10004/lot-9fd6e1a5-8e40-4e15-87c5-a3f80180d40e

[MikB]

It's a prismatic. By swinging the prism so that it sits over the glass above the card, you can sight an object using the 'lubber' (?) line on the cap glass through the slot in the prism carrier, and read the bearing to about 1/2 a degree through the lens and prism.

I *think* the maker is French Ltd., but there were many producing these instrunments.

It's a 'dry' compass - there's no fluid damping of the swing; you have to use the little button to drag the oscillation to a stop.

I've seen some websites going on about residual radioactivity from the radium paint, which was originally luminous. I still don't really know what to think about that, but I'd say DON'T take it to bits to expose the radium paint - see here:-

http://www.trademarklondon.com/Radiation/index.html

I've got a Cruchon & Emons Pattern VII which is as accurate as a modern Silva sighting compass I have, and much more so than my US army issue lensatic.

[Chasemuseum]

A quick comment on radium. It may still be present even if the instrument no longer glows in the dark. In use it is mixed with rare earths (like inside an old TV tube). the radiation causes the rare earths to phosphor (glow in the dark). This is a manufacturers economy, radium was very expensive and they needed very much less in the paint if they did this. So when an instrument no longer glows this may just be a factor of the rare earths not the radium. If the material is on the outside of the instrument it may be encapsulated with a small amount of nail clear polish. If its inside the instrument (watch face & hands) leave them alone.

The link above is very good as a quick summary. Radiation is in three parts - alpha, beta & gamma. Radium emits alpha & gamma. Alpha is the super nasty radiation - it will not penetrate human skin or a sheet of paper however if you ingest it as dust (breath in, touch with hands and then hand to mouth or contaminate food/drink) it is exceptionally nasty. Hence all the instructions about encapsulation and leaving alone if sealed inside an instrument.

The link above also raises the issue of arsenic - this is a Victorian problem rather than WW1. Arsenic was commonly used as a part of green dyestuff through the c19 - particularly in wall-paper. Not relevant to WW1 but if you do handle Victoriana beware of what may contain arsenic and unlike radioactive materials with a half-life and ultimately becoming safe, arsenic is never safe.

Cheers

RT

PS I said that radium is nasty. The old unit of radiation was the Curie. This is the radiation emitted by 1 gram of natural radium. When mining natural uranium, it is reduced to uranium oxide, commonly known as "yellow cake". The yellow cake enters a stable decay cycle, with various radioactive isotopes being created by the decay of the uranium and these in turn decay to produce other radioactive daughters and ultimately yield stable isotopes. When the equations for stable decay are resolved the radioactivity of 1 tonne of yellow cake is 3.7 curie. That is radium is about 300,000 times more radioactive than uranium oxide.

Old watch and instrument factories routinely have uranium and radium contamination issues. Not a good idea for an apartment conversion. The old radium smelters are really bad news - here in Sydney the smelter was at Hunters Hill. Additionally the coke plants next to the old gas-o-meters in the days of "town gas" in the public gas works, also usually have radium contamination in their waste pit areas. These are where the real urban radiation hazards are, not in a few old watches, compasses and radios.