Comments on: The Analemmas of Vitruvius and Ptolemy http://myreckonings.com/wordpress/2007/10/28/12/ Lost Art in the Mathematical Sciences Tue, 06 Jan 2009 11:21:14 +0000 http://wordpress.org/?v=2.2.1 By: Tristan http://myreckonings.com/wordpress/2007/10/28/12/#comment-627 Tristan Fri, 21 Nov 2008 16:34:06 +0000 http://myreckonings.com/wordpress/2007/10/28/12/#comment-627 <p><p>Thanks for this excellent page. I have to illustrate the difference in shape between a summer and winter solstice shadow arc as part of a natural navigation course that I teach and it is the part of the course that fascinates and confuses as dependably as any other.</p><br /> <em><p>Your welcome–I appreciate the time you took to comment. This essay is without doubt the most arcane of any of them so far, so it’s nice to hear from someone who shares an interest in the subject.</p><br /> <p>BTW, you have a fascinating site and blog (or "Log"). Solo Atlantic crossings by flight and by sail, mountain climbing, expedition leader on five continents--incredibly impressive. I have an armchair interest in "natural navigation," actually. There's a fundamental conflict between my inner ear and the sea, though. I tell people I'd love to sail but I could only do it if when there was no wind 8^). But I have books on nautical navigation by natural and celestial means, including both editions of David Burch's book "Emergency Navigation." I originally intended to follow my book on mental calculation ("Dead Reckoning: Calculating Without Instruments") with another "Dead Reckoning" book on using these calculating methods to help in actual dead reckoning navigation, probably mostly on land. Someday I will. Meanwhile, I've spent the last hour engrossed in your blog and links, and I've added your blog to my list of ones to follow. Thanks for that! — Ron</p></em></p> <p>Thanks for this excellent page. I have to illustrate the difference in shape between a summer and winter solstice shadow arc as part of a natural navigation course that I teach and it is the part of the course that fascinates and confuses as dependably as any other.</p>
<em><p>Your welcome–I appreciate the time you took to comment. This essay is without doubt the most arcane of any of them so far, so it’s nice to hear from someone who shares an interest in the subject.</p>
<p>BTW, you have a fascinating site and blog (or “Log”). Solo Atlantic crossings by flight and by sail, mountain climbing, expedition leader on five continents–incredibly impressive. I have an armchair interest in “natural navigation,” actually. There’s a fundamental conflict between my inner ear and the sea, though. I tell people I’d love to sail but I could only do it if when there was no wind 8^). But I have books on nautical navigation by natural and celestial means, including both editions of David Burch’s book “Emergency Navigation.” I originally intended to follow my book on mental calculation (”Dead Reckoning: Calculating Without Instruments”) with another “Dead Reckoning” book on using these calculating methods to help in actual dead reckoning navigation, probably mostly on land. Someday I will. Meanwhile, I’ve spent the last hour engrossed in your blog and links, and I’ve added your blog to my list of ones to follow. Thanks for that! — Ron</p></em>

]]> By: mina.jain http://myreckonings.com/wordpress/2007/10/28/12/#comment-576 mina.jain Thu, 28 Aug 2008 05:44:58 +0000 http://myreckonings.com/wordpress/2007/10/28/12/#comment-576 <p>Like to get information on Gammon design for a historic largest sundial.</p> <p><em>I'm not that familiar with huge sundials, but I do know that quite a few sundials claim to be the largest in the world. I have often read of the one in Jaipur in India, and there is a nice walkthrough of it online <a href="http://www.bomhard.de/englisch/jaipur/00.html" rel="nofollow">here</a>. I understand that the biggest problem with huge sundials is the diffraction of light that prevents greater accuracy beyond a certain size, but I'm afraid I don't have any specific material or background on designing large devices like this. --- Ron</em></p> Like to get information on Gammon design for a historic largest sundial.

I’m not that familiar with huge sundials, but I do know that quite a few sundials claim to be the largest in the world. I have often read of the one in Jaipur in India, and there is a nice walkthrough of it online here. I understand that the biggest problem with huge sundials is the diffraction of light that prevents greater accuracy beyond a certain size, but I’m afraid I don’t have any specific material or background on designing large devices like this. — Ron

]]> By: liunian http://myreckonings.com/wordpress/2007/10/28/12/#comment-151 liunian Sun, 24 Feb 2008 16:11:36 +0000 http://myreckonings.com/wordpress/2007/10/28/12/#comment-151 Geometric constructions is the first.I think you can find out good method for 5 and 6-parameters formula. Geometric constructions is the first.I think you can find out good method for 5 and 6-parameters formula.

]]> By: Jim http://myreckonings.com/wordpress/2007/10/28/12/#comment-20 Jim Thu, 17 Jan 2008 04:17:16 +0000 http://myreckonings.com/wordpress/2007/10/28/12/#comment-20 <p>Ptolemy used 23d 51m 20s for the obliquity of the ecliptic. The correct value at that time was about 23:40:33.</p> <em><p>Thanks, Jim, that couldn’t have helped his results. I’m surprised Ptolemy was so far off on this–--perhaps he assumed that past measurements were still valid. --- Ron</p></em> Ptolemy used 23d 51m 20s for the obliquity of the ecliptic. The correct value at that time was about 23:40:33.

Thanks, Jim, that couldn’t have helped his results. I’m surprised Ptolemy was so far off on this––perhaps he assumed that past measurements were still valid. — Ron

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