Talk:Bris sextant

The "Bris sextant" is a sextant in the normal usage of the word, and it is a true "instrument of reflection" obeying the same optical principle of double reflection found in the common octant and sextant. But does it deserve to be called a sextant? Doesn't that word demand that it be able to measure angles up to 120 degrees? Etymologically, yes, but etymologies are not the meanings of words. The meaning of the word sextant has evolved to cover other instruments for measuring astronomical angles for navigational purposes. For example, the sextant on the Apollo spacecraft could only measure angles up to about 60 degrees, yet no one complained that it was not "really" a sextant because of that. Or consider a typical aviator's bubble sextant used from the 1930s through the 1970s on tens of thousands of aircraft. Most designs for such bubble sextants did not use double reflection at all and few could measure angles above 90 degrees, and yet these are still called sextants without any resulting confusion and without any serious complaints about the true meaning of the word. The topic of this article, the Bris sextant, is a sextant in some ways more than the Apollo sextant or the aviator's bubble sextant. It is a "fixed angle" sextant but otherwise it operates in most respects just like a standard marine sextant. For example, the navigator must remember to "swing the arc" to ensure that the angle is measured perpendicular to the horizon. In addition, the navigator must ensure that the line of sight is collimated (made parallel to the plane that is perpendicular to the surfaces of the reflective pieces of glass) by rocking it side to side. Like a common marine octant or sextant, because of the double reflection, the "Bris sextant" is immune to pitching motions due to motions of the observer's hand or rolling of the vessel and as a result it can be accurate to the limits of resolution of the human eye (approximately one minute of arc). The two big differences between this simple device and those other more flexible instruments is that the Bris sextant is a fixed angle instrument and also, because the reflecting surfaces are not opaque, it can have more than two reflecting elements (three in the original design).24.148.18.151 (talk) 05:32, 25 October 2010 (UTC)

= Journal article = There is a journal article written on operation of the Bris sextant which fully describes it's operation by proof. I believe it is in a Physics journal. It can be found via Google Scholar, although it is a for-pay article so not available free. Jcline0 (talk) —Preceding undated comment added 16:00, 29 July 2012 (UTC) * This is the paper:  Physics Teacher April 2000 Vol 38, Issue 4, "Easily constructed mini-sextant demonstrates optical principles"   Jcline0 (talk) 15:43, 1 August 2012 (UTC)