NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: the Quintant
From: Dan Allen
Date: 2002 Jul 6, 08:11 -0700
From: Dan Allen
Date: 2002 Jul 6, 08:11 -0700
I agree with your thinking George. I have a qunitant made by Fuji around 1900. It has no other markings on it other than "Fuji #372". The scale is actually calibrated to 150 degrees, slightly past the 144 degrees that qualify it for quintant status. It is very similar to sextants of the period appearance-wise, and if glanced at quickly one would never know it is a quintant. Dan -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of George Huxtable Sent: Saturday, June 22, 2002 12:41 PM To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM Subject: the Quintant When did the Quintant first appear, I wonder? Can Nav-L help to answer this question? The quintant is a development of the sextant, the scale subtending 72 degrees (a fifth of the circle: hence its name) and measures angles up to 144 degrees, compared with a sextant which has a scale subtending 60 degrees (hence its name) and measures to 120 degrees. Quintants may have been intended for surveying by horizontal sextant angles, as much as for widely-separated lunar distances. They were being offered, as "surveyor's quintants" right into the 1930s. A great proponent of the quintant was Lecky, in "Wrinkles", which went through many editions in the later part of the 19th century. I had always thought of the quintant as a 19th century instrument, intended to extend the range over which lunar distances could be measured. However, these views of mine have been considerably shaken by the recent appearance of Vol 1 of "The Malaspina Expedition", a translation of Malaspina's journal 1789-90, edited by Andrew David et al (Hakluyt Society, 2002). This contains references on page 240 (and also 247) to the use of a quintant, not for taking lunars, but for measuring the altitude of the Sun, when the vessel was close to land in the direction of the Sun. In that case, a clear horizon below the Sun could not be seen, and the observer was driven to observe the angle between a high sun and the horizon in the opposite direction, using instruments that would measure more than 90 degrees. In translation, Malaspina's words were- "Since the short distance at which we were sailing off the coast made it difficult in the morning and even at noon to get a horizon clear enough for taking sights, the method of back-observations began to be preferable both for observing hour angles and meridian altitudes. Sextants, and even more a Wright's quintant belonging to Don Juan Vernacci were on this occasion most useful since the Sun, being close to the zenith, very soon reached the arc of elevation subtended by the arc of the quintant". Malaspina was 9 degrees south of the Sun at noon, and the Peruvian coastline was close north-east of him. To me it seems clear that he was measuring Sun altitudes up, not from the horizon below the Sun, but from the opposite horizon, so requiring an instrument capable of measuring more than 90 degrees: facing away from the Sun and measuring its altitude behind the back of his head. In a footnote concerning this passage, Andrew David refers to a quintant rather as I have described it above, and then goes on to say- "This particular instrument was possibly the modified version of the Hadley quadrant designed by George Wright in about 1780, in which the index mirror could be slewed through 45 degrees for making a back observation. For a full description of this instrument see Charles H Cotter, A History of the Navigator's Sextant Glasgow, 1983, pp 136-7." The mystery deepens a little here. Andrew David has correctly followed Cotter's description of the George Wright instrument, including the slewing of the index mirror by 45 degrees, but this seems to be contradicted in Cotter's own diagram, which appears to show the index mirror reversed back-to-front, ie slewed through 180 deg, not 45 deg. As far as I am able to judge, the George Wright instrument could measure altitudes between 0 and 90 deg in one range, and then by making an adjustment, the "back" altitudes of 90 to 180. (The difficulty with using such back observations was always that of correcting for the index error.) Cotter doesn't refer to the George Wright instrument he pictures as a quintant, and to me that word doesn't seem applicable in any way to that instrument, as there's nothing in it to correspond to a fifth of a circle. So I doubt if the George Wright instrument pictured in Cotter is the "Wright's quintant" referred to by Malespina. On page 206 of the Malaspina translation, there's a list of the sextants carried on the vessel, including one by Wright. A translator's footnote refers to this as being by Thomas Wright, but might Malespina perhaps be referring to the same instrument as the "Wright's quintant" of page 240? If so, which Wright was the maker? I have enquired whether the word "quintant" is what was actually used in the original Spanish text, or perhaps introduced in translation as a word embracing wide-angle measuring instruments, and Andrew David has been kind enough to confirm that the original Spanish text reads "Los Sextantes, y aun mas un Quintante de Wright propio de Don Juan Vernacci." Malaspina's words about the observation, quoted above, provide a further puzzle. At the date of the observation of page 240, 23 Sept 1780, the Sun was close to the equator, and the vessel was at latitude 9 degrees South, or so. So around Noon the Sun's altitude would have been about 81 deg, and its elevation above the backwards horizon would have been 99 deg, well within the 120 deg range of a sextant. As the afternoon progressed, the azimuth of such a high Sun would change very quickly, and it would become visible above the clear horizon to the NorthWest, long before it had fallen enough to put its backward altitude out of reach of a sextant. During that day, the only time a quintant would provide an advantage over a sextant, as I see it, would be in enabling backward altitudes to be measured before 9am or so, local time. So what did Malaspina imply, when he stated that the quintant was useful "since the Sun, being close to the zenith, very soon reached the arc of elevation subtended by the arc of the quintant"? This doesn't make sense to me. I just don't see what advantage a quintant would have provided over a sextant, when the Sun was close to the Zenith, on that day or any other. The quoted passage above would to me make much more sense if Malaspina had intended to say something like "... the Sun, being on a path which would take it close to the zenith ...", rather than "... the Sun, being close to the zenith ..." If that was indeed Malaspina's intended meaning, then the whole passage would become compatible with the existence at that date of a real quintant, of the type which later became familiar, measuring to 144 degrees. It would confirm the early existence of such an instrument. I think the existence of a quintant, and the name "quintant", as early as 1789, would come as something of a surprise to many historians. The advantage of a quintant would then have shown up in allowing Malaspina to make Sun altitude measurements that day using the back horizon, much earlier in the morning than would have been possible with a sextant. I wonder if Nav-L members are aware of any early quintants in museum collections in their area, or perhaps references to quintants in early editions of (for example) Bowditch. Any ideas and suggestions would be welcome. I have already tried the "rete" list (on the history of scientiic instruments). Thanks to Andrew David for providing helpful information. George Huxtable. ------------------------------ george@huxtable.u-net.com George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. Tel. 01865 820222 or (int.) +44 1865 820222. ------------------------------