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I recently acquired a an5851 bubble sextant.  As far as I can tell, it is
fully functional but being un tutored in its use, I am having some
difficulties so permit a few questions from the uninitiated....

1) I found a manual (dated 20 March 1945) on the web with pages i to v and
1 -16.  This seems like the front of a bigger manual since these pages
offer little more than a description and the introduction promises 'This
manual contains instructions for the Installation, Operation, Maintenance,
and Overhaul..."

1a) Are these pages really all that exist or is this just the front of a
bigger manual?

1b) Is there any source for the complete manual?

2) Let me describe what I see when I form a bubble and look through the
instrument.  The bubble looks like a black well defined dot with a clear
transparent spot within it.  I can remove the bubble completely and form a
new one of varying sizes.  Small bubbles (say smaller than six Sun
diameters or two minutes) are sluggish and don't respond well to movements
of the sextant.  The clear spot is not exactly centered and moves about
within the black dot.

I have been using the clear spot as a peep sight and centering the target
within it.  On one occasion with a large bubble I did observe a reduced
sized image of the target (sun) in the center of the dot (which did not
coincide with the clear spot).  I have also seen the whole dot to be
illuminated when the sun was in its center.

2a) So how big a bubble should be used?  How many sun diameters?

2b) What is the recommended observational method?

use clear spot as peep sight?

guess where center of dot is and align with target?

other?

2c) is the bubble acting as a lens collecting light and concentrating it
within the clear spot?

Any insights you can provide or pointers to existing information on these
questions would be greatly appreciated.

Mike Dorl
Madison WI

   

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