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On Sun, 14 Dec 2008 03:41:37 -0700, George Huxtable   
wrote:

> However, it seems to me at least plausible for a 2-mirror instrument  
> (which
> couldn't, any longer, be called a sextant) to be designed, which could
> measure angles from zero to 180º, though nobody ever seems to have done  
> so.
> That's material for another posting.

George,

You might take a look at this instrument from the Smithsonian (National  
Museum of American History)  Physical Sciences Collection - Surveying and  
Geodesy; Alidade (reflecting) by G. Dolland PH*319452: (see 35 KB  
attachment)

The mechanism is such that the angle between the rule edge and the  
adjusting (index) arm edge is the same as that between the line of sight  
through the aperature over the "horizon" mirror to the first object, and  
the reflected line of sight to the second object.  This is set around 25  
degrees, I think.

There is a very similar instrument in (if I recall correctly) in one of  
the British museums; opened to a wider angle, close to 60 degrees.

I have not been able to find out what the inventor called the various  
parts, but I hope you can follow my description while looking at the  
illustration.

-- 
Richard . . .

Using Opera 9.2.4 after the "Dog" died
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