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Geoffrey wrote:
> I also have a British Mk IX bubble sextant. I am afraid I do not share
> Robert Eno's high opinion of this sextant, or its successors, as ".... the
> best bubble sextants ever made. Period." Personally, I find them clunky
> and overcomplicated - too much potential for things to go wrong. There is
> a tendency for the 5 degree increase mechanism to be stuck on these
> sextants, which means taking the thing apart. Thankfully, people who have
> gone through this exercise have put their experiences onto websites and
> full instructions on how to do this can be downloaded.


Robert responds,

I guess I have been lucky. I own three of them and aside from the fine
setting knob having to be unstuck, or more correctly, re-lubricated, I have
had no problems whatsoever with my MK IX sextants. I agree that they are
complex instruments and perhaps I should have emphasised this in my
description of the cons, however, in my experience, they are good sextants
and have given me long years of service.

If I were to be dropped into the middle of nowhere (on land) with only a
sextant and compass to guide me home, would I take a MK IX? No. I would take
a marine sextant with a C.Plath bubble attachment because both are easy to
fix and calibrate.

My ideal bubble sextant would entail a MK IX bubble system housed in a unit
which could be clamped onto a marine sextant in place of the telescope. The
late John Luykx, who was an authority on bubble sextants and who owned an
extensive collection of these, was considering the idea of making such a
device but didn't have the heart to cannibalize any of his precious MK IXs.
He and I shared a great enthusiasm for the MK IX.

Geoffrey wrote:
>Though the Mk IX has a bewildering multiplicity of knobs and levers, they
>are all easily accessible without having to take your hands off the two
>handles. The averaging system in these sextants is probably more trouble
>they they are worth when used in ground based observations.

Robert responds:

I believe we had a discussion on this some time ago. For purposes of taking
observations on land, it is recommended that the averaging mechanism not be
employed, although you do have to wind it to disengage the shutter which
blocks the path of light when the averager winds down.  Some owners just
remove the averaging mechanism and shutter as the mechanism only add useless
weight to the instrument. I have kept the averaging devices on mine simply
for the collector/historical value.

Geoffrey wrote:
>
> One thing Robert puts great emphasis on is the ability of the Mk IX type
> sextant to shoot faint (2nd magnitude) stars. He goes on to tell how he
> was able to take a fix on the Hale Bopp comet and says, "Try that on any
> other bubble sextant."

Robert responds:

Indeed I do. Here is why: the MK IX illumination system is set up such that
when the bubble chamber is illuminated, only the circumference of the bubble
chamber and the bubble are illuminated. Contrast this to say, the Plath
bubble attachment and most other bubble sextants where the illumination
system lights up the entire bubble chamber and essentially washes out all
but 1st magnitude stars. I hasten to add that I have found that the Kollsman
periscopic sextant has a nice illumination system that comes close the MK
IX.

Geoffrey wrote:

Well, I suggest Robert tries it
> with an A-12, which has just a single piece of clear glass between eyeball
> and star, compared with the Mk IX type which has two mirrors and a piece
> of clear glass between eyeball and star. Basically, with the A-12, if you
> can see it, you can shoot it.

Robert responds.

I have not had the opportunity to use an A-12 Geoffrey, but your other
comments on it almost scares me away:
------
"my conclusions are that they generally need taking apart, cleaning and
rebuilding. The bubbles (there should be two with each sextant)
generally need refilling. Refilling the bubbles needs a "Bristol"
headed screwdriver - not generally available, certainly outside the
USA - which means making your own. Modern batteries will not fit into
the bubble illuminator, which means machining out the bulb holder to
accept modern batteries. Not difficult if you have access to a lathe.
Impossible if you do not. The bubble reflecting mirror is front
silvered on these sextants and they are usually in poor condition
after 60 odd years, requiring re-coating with aluminium and
preferably overcoating with a layer of quartz so they can be cleaned
without damaging the coating."
-------
Nevertheless, I have been contemplating the acquisition of one for some time
but have been deterred the condition of the units I have seen. Several year
ago, when I was visiting friends in the Annapolis area, I made my usual
pilgrimage to a well-known second hand nautical shop. They had a Link for
sale but it was in abysmal condition and I just wasn't willing to pay a lot
of money for something I knew I would have to fix with unpredictable
results. I have been eyeballing the one listed in the Celestaire catalogue
but may have to wait until the kids grow up and I retire to become a
dilettante.

I wonder if you would mind describing the Link A-12 illumination system for
me?

Happy New Year to all by the way.


Robert



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