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Bill,

Indeed, the notion of "full sized sextant"
apparently evolved:-)
Nowadays, the largest sextants still in production
have arc size 162mm (according to Celestaire catalog).
And they are considered "full-size".
That is a bit less than 6 and 1/2 inches.
A great authority of late XIX century (Lecky)
on p. 70 of his book "Wrinkles of practical navigation",
says: "Avoid a sextant of less than 8 inches radius".
And then he mentions
"...The writer's instrument is a 10-inch Troughton
divided on platinum".

Let me add few comments of my own.
I am really interested in this question whether
the best XIX century sextants (made for the Lunars)
were better than out modern ones.

I have no way to decide this. I cannot afford a
"10-inch Troughton divided on platinum"
in decent condition to test it.
So I have a modern Russian CNO-T, 6 and 1/2 inch
and a 1900-or-so C. Plath, 7 and 1/2 inch.
The modern one is VERY much superior...
in all respects.

Alex.

On Wed, 25 Apr 2007, Bill wrote:

>
>
> Interesting.  Could not quickly locate a reference to "full-sized sextant"
> in my library so Googled it.
>
> I find the following arc radii described as "full sized:"
>
> 8"
> 178mm
> 7"
> 6.5"
> 162"mm
> 6"
>
> Quite a range.  If we consider 162mm to be full sized, the Astra then
> becomes a 17/18ths (large yacht ;-) size.
>
> If we consider Davis's 178mm to be full sized (which approximates the 7"
> figure I recall), then the Astra is indeed a 7/8ths yacht size.
>
> That all reminds me of a pizza bet with my father.  I bet him my 10-year-old
> 1975 "mid-sized" Chevy Nova automobile was longer than his new full-sized
> Buick Century.  I won by 2".
>
> Bill
>
>
>
>
> >


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