NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Heath vernier sextant
From: Stan K
Date: 2012 Jul 23, 19:45 -0400
From: Stan K
Date: 2012 Jul 23, 19:45 -0400
Alex,
-----Original Message-----
From: eremenko <eremenko@math.purdue.edu>
To: NavList <NavList@fer3.com>
Sent: Mon, Jul 23, 2012 1:47 pm
Subject: [NavList] Re: Heath vernier sextant
From: eremenko <eremenko@math.purdue.edu>
To: NavList <NavList@fer3.com>
Sent: Mon, Jul 23, 2012 1:47 pm
Subject: [NavList] Re: Heath vernier sextant
Stan, > I have been playing in the sunlight (at least between the rain showers), > and the key, at least for me, seems to be getting the light source at the > correct angle with respect to the diffuser. Yes. Did you clean the arc and the vernier? I mean with a piece of slightly oiled cloth? No, I did not, but I will. Did you shift the microscope back and forth to achieve the maximum magnification? Yes, I did, but it really wasn't much help. I still had difficulty determining which line aligned with which line. In most sextants I've seen the vernier is readable after you do this, in daylight, even if there are dense clouds. That is what we are suffering with right now, so I took the sextant outside and tried it. Even with clouds it is easier to read outside than inside with any kind of illumination. > BTW, what color LEDs did they use in 1940? They used an ordinary lamp. And long before that, they used an oil lamp. I've seen (photos of) several sextants (and repeating circles) of XIX century equipped with oil Lamps. And they went blind within a year. By the way, I suppose that most of the observations in actual practice were made in daylight. Including Lunars. A saving grace.
Lecky (late XIX century) strongly recommends sextants with large arc radius. I can certainly understand why. Contrary to his recommendations, most of the sextants in XX century were made with relatively small arc radius of 6 1/2 or 7 inches (I suppose because of the frame rigidity considerations). Hey, it was a gift. I can't complain about the arc radius . I used to have a C. Plath circa 1911 with 10" vernier scale and 6 1/2 or 7 inch radius, and reading it was a real pain:-) Ah, I am not alone. But the reason why I sold it was not that, but insufficient frame rigidity. I own a pocket sextant with scale of 2 1/2 inch radius, divided to 1' with a vernier, and it is somewhat hard to read. I'll bet, but pocket sextants are not expected to give great resolution. But they seem to be neat devices. Unfortunately I have only seen pictures and read about them. Alex. Stan