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Herbert Prinz wrote-

> Thank you for the images of your Bris Sextant (does it actually deserve
> the name 'sextant' ? It's some kind of a goniometer).

I agree with Herbert. It's not a sextant, by ANY definition. To qualify as a
sextant, the arc of which occupies a sixth of a circle, it should measure
angles up to 120 degrees. The Bris device does not do so, nor does it allow
arbitrary angles to be measured, just a few spot values to be compared.
Another name than sextant needs to be agreed on. Any suggestions?

It seems a clever little device, which may well have its uses. For example,
if it has sufficient long-term stability,  it could perhaps provide some
calibration checkpoints for a true sextant, over part of its range..

What about the dark glass that's used at the side that faces the Sun?
Presumably, that has to be dark enough to make it comfortable to view the
Sun image. Agreed, the brightness of that image is reduced somewhat by the
dimming of reflections in the unsilvered glass, which means that a less-dark
outer glass may be acceptable, compared with the shade required for a
sextant. But my concern is this; that the horizon, also, has to be viewed
through that same dark glass, and unless the horizon is particularly clear
and bright, it won't be seen sharply enough for a measurement. Is that a
handicap, in practice?  Is there, or could there be, an additional shade
glass on an arm, to put it just in the way of the light from the Sun,
without darkening the horizon view?

Another question that's puzzling me a bit, and I'm still trying to visualise
it. There's nothing (presumably) to define where your eye is to go, such as
is provided by the eyepiece of a sextant or the peep of some octants. Is the
device then subject to some sort of "collimation error", if the eye is put
at the wrong place? If not, why not?

George

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

Another question. Can you improve the accuracy achievable with such a
device, by holding it (or strapping it with sticky-tape) in front of the
objective of a sextant's telescope?

George.

   

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