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I suggest that Hanno curbs his enthusiasm for copying a Bush horizontal
mirror for a bit, while he ponders on some of its snags.

A hard look at the patent specifications, (1912358), might perturb him, as
it perturbs me.

Just setting to one side the question of its dynamic performance to changes
in tilt and acceleration, consider only its static behaviour, after it has
been sitting in a steady position for as long as necessary for everything to
have settled. The aim is to end up with the mirror, #59, accurately
horizontal. How is that to be achieved?

I refer to components as numbered in the three diagrams that form part of
the patent . The assembly #51, to which the mirror is rigidly coupled,
appears not to have any pendulous property in itself. There's no
ballast-weight to tell it which way is up. Instead, it appears to take its
sensing of the horizontal entirely from its coupling with the spherical
container #35, within in which it sits. For the purposes of this argument,
we will assume that somehow #35 has managed to make its own equator exactly
horizontal, because of the way it's ballasted and floating on Mercury. How
does #51 then contrive to follow it? Only by means of its coupling of four
light springs #53, connected very close to the centre of the triangular
assembly #52.

That angular coupling has deliberately been made flexibly weak (for
dynamical reasons), just where (for statical reasons) it needs to be firm
and precise. Remember, any tilt of the mirror from the horizontal, of more
than a very few arc-minutes, would devalue the instrument for its intended
purpose.

Hanno should contemplate, hard, how he would actually implement that
mechanical arrangement to ensure that the mirror-plane corresponds precisely
to the equator-plane of #35, especially in the absence of any
fine-adjustments, which are nowhere to be seen.

The whole notion is impractical and flawed, which presumably explains why it
was not made. I hope my words will save Hanno from much wasted effort.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
----- Original Message -----
From: "Hanno Ix" 
To: 
Sent: Thursday, August 20, 2009 4:34 PM
Subject: [NavList 9574] Re: The development of bubble sextants



I also like making things, and making them well. A usable gyro, mechanic or
otherwise, would exceed my capabilities by far, a bubble spirit - even a
DoubbleBubble - would not. And I would be thrilled if I could build a bubble
spirit that is significantly more stable than the ones known sofar -- no
matter the practical use.

As far as practical navigation: gyros have such superior properties which
never could be matched by any bubble spirit. They can seek North for once, a
spirit level never could.

Do I sense, though, that you have come to agree with the concepts of Bush's
idea?

I'd be delighted.

H


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