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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Hooke's Quadrant
From: Kieran Kelly
Date: 2004 Jan 29, 10:30 +1100
From: Kieran Kelly
Date: 2004 Jan 29, 10:30 +1100
I have just completed Stephen Inwood's very informative, if a bit long winded, "The Man who Knew to Much" the life of the extraordinary English scientist Robert Hooke (1635-1703). Very informative on a host of matters. I bet few know that the universal joint which sits under your car and connects the drive shaft to the transmission (in a rear wheel drive car) was invented by Hooke in about 1660 and was first fitted to an Astronomical Quadrant. Also I had thought previously that the reflecting quadrant was invented by Isaac Newtown and perfected by Hadley and from there it morphed into the sextant. Not true. Hooke invented the first reflecting quadrant in 1666 (as opposed to the Backstaff Quadrant) and even fitted it with a tangent screw as well as coming up with plans for an endless tangent screw. (Peter Ifland's excellent "Taking the Stars" gives Hooke his due on page 13, with a diagram of his instrument.) One thing which caught my eye and which I invite comment is the passage in the Hooke book which says "Accuracy to one second of arc in a hand held instrument was not achieved until the early 1920's, when the Swiss instrument designer Heinrich Wild produced the Wild Universal Theodolite" (Page 88). Is this true? Was there never a sextant made before this date that could measure to the second? Has there been one made since? I checked a couple of modern sextants which measure respectively: Plath Classic 1/10 minute 6ss Plath Professional 1/10 minute 6ss Freiberger Yachtsman 1/60 degree 1 minute F M Barker Box Sextant 1/60 degree 1 minute (Vernier) Why can't a sextant be graduated to the second? It would simply be a matter of scribing the micrometer drum more closely and possibly adding a magnifying viewer. Magnifiers were standard on vernier sextants for years. Is it because it was considered impractical to go down to a second on a hand-held instrument? Your advice would be appreciated. Also on a recent post I asked if anyone was aware of sextants being cast in bronze other than the Plath Classic and Royal. Why would you cast in bronze? What is the advantage over brass? Regards Kieran Kelly Sydney Australia