John I think the base is such that either an Astro Compass could be mounted - or a normal magnetic compass with the same fitting. The screws on the side of the mount are connected to two little magnets inside the base. These are used to compensate for the magnetism of the plane's fuselage. I would STRONGLY advise not to try to disassemble the base - I managed to damage mine - made of softish brass - while trying to get inside…. If the screws still work and move the internal magnets, you should be able to detect that with a common magnetic compass. Trust that this helps
Best regards Kevin Karney Freedom Cottage, Llandogo, Monmouth NP25 4TP, Wales, UK 51° 44' N 2° 41' W Zone 0 + 44 1594 530 595 On 27 Feb 2012, at 02:36, John Pickard wrote: > Good morning, > > I have an Astro Compass mark II in excellent condition, made by Sperti > (Cincinnati) and when I bought it, it came with a base made by Dominion > Electric Protection Co of Canada. I also have a second base (bought from a > junk shop in Australia) engraved "RAAF G5A/366" and "AWA 891". From this, I > assume that it was made by Amalgamated Wireless Australia (Sydney, Australia) > for the Royal Australian Air Force. But the two bases are quite different as > seen in the attached images. > > The Canadian base is hollow tube with a black crinkle finish while the RAAF > base is painted grey, but more significantly, it has a cylinder fitted in the > bottom, retained by brass screws countersunk into the tube of the base. Four > knurled brass knobs in the side of the base are arranged at 90o intervals, > with two higher, and two lower on the base. Removing these reveals holes with > square pegs. These pegs are obviously meant to take some sort of adjusting > key. > > While I could dismantle the cylinder from inside the base, I'm reluctant to > do this until I have a better idea of the function of the cylinder. > > The Sperti instructions make no reference to such a base, and all the other > instructions and illustrations I could find on the web show a hollow base: > > Instructions: http://myjunkshop.com/astro/astronew.html are an older version > of the same Sperti instructions that I have. Instructions by W.W. Boes & Co > (Dayton) (http://www.scribd.com/doc/3856694/AstroCompass-Manual BEWARE of > numerous pop-ups etc. that are impossible to kill) show a base without the > four knurled knobs in the side, i.e. it is the same as the Canadian base. > > Illustrations: http://www.prc68.com/I/AC_D500.shtml show the Sperti hollow > base, and those at > http://cadrans-solaires.pagesperso-orange.fr/navigation/astrocompass/astrocompass_uk.html > show a similar hollow base. > > Does anyone have any idea of the function of the cylinder fitted into the > base made for the RAAF? If the Astro Compass were a magnetic compass, I would > imagine that the square pegs were for adjusting out magnetic influences when > fitted inside a vehicle or aircraft. Such adjustment screws are standard in > e.g. aircraft standby magnetic compasses, and are used when "swinging the > compass". I did this myself when I had such a compass mounted in my Landrover > years ago (and it was surprisingly accurate). But such adjustment seems > counter-intuitive and unnecessary in an Astro Compass. > > > Many thanks, John > > John Pickard > john.pick...@bigpond.com > <Canadian and AWA bases top view tiny image.JPG><AWA base bottom view tiny > image.JPG><Canadian and AWA bases side view tiny > image.JPG>--------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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