A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Cleaning arc of Vernier sextant.
From: Robert Eno
Date: 2006 Oct 28, 11:37 -0400
From: Robert Eno
Date: 2006 Oct 28, 11:37 -0400
I have been silently following this thread for the last few days. One wag alluded (in a jovial manner, I am quick to add) to our friend George being somewhat of a Luddite and/or overly-thrifty by congratulating him on taking the plunge into the world of quality metal sextants. If such is the case, I have to ask George the obvious question: George, once you decided to acquire a metal sextant, why didn't you just go the whole way and purchase a micrometer drum sextant? Then you would not have to concern yourself with stockpiling other people's cigar ashes or going through the painful tedium of trying to read a vernier scale under poor light conditions. I look forward to someday reading about George's acquisition of a proper micrometer drum sextant. The saga continues..... Robert ----- Original Message ----- From: "Henry C. Halboth"
To: Sent: Friday, October 27, 2006 11:45 PM Subject: [NavList 1494] Re: Cleaning arc of Vernier sextant. > > To all, > > Frank has asked how the sextant arc and vernier was polished with ashes. > I know of no technical dissertation on the subject, but can state my > experiences with the caveat that there well may be other ways - under the > general heading "different ships, different long splices". > > Being a smoker in those days, I kept a little tin of cigarette/cIgar > ashes. or fag-ash as George has so wonderfully said, carefully sorted > through to insure no unburned or other contaminating residue - actually > my recollection is that cigar ash formed the best and finest abrasive. To > use, one simply touched a finger draped bit of fine cloth to the ash and > ran it lightly over the arc until the desired luster was obtained. In the > shipboard environment, the cloth was probably sufficiently damp for the > ash to adhere, whereas, in a low humidity environment it would probably > be appropriate to dampen the cloth a bit. This method of polishing a > sextant arc is certainly not a figment of my imagination, although I > cannot with certainty say whether I read it in some obscure publication > of yesteryear or if it was passed to me by word of mouth. > > George has mentioned the difficulty in obtaining sufficient lighting to > read-off the vernier of a sextant. There is no question but that accuracy > in reading-off is significantly affected by the lighting employed. Not so > much the actual light or its intensity, but rather the angle at which it > strikes the vernier/arc interface. The light source, whether it be the > sun or lamp, should be so positioned that the maximum intensity is > directed along the index arm at right angles to the vernier/arc > interface. In the daytime, this does not present much of a problem; all > one need do is step out of the chart house and direct the sunlight > appropriately - as a matter of fact, the frosted glass panel usually > affixed to the index arm, just above the vernier, is for the purpose of > diffusing that sunlight to dampen excessive reflection from the arc while > reading through the magnifier. At night, or at twilight in taking star > sights, one must of course use the chart table light or some other > convenient source; again the light must be directed along the index arm > and the sextant manipulated so as to obtain the maximum intensity at the > interface. After a time, it all becomes second nature and no great > problem. It may well be that at least some of the reticence to star > sights or other night observation originated in lighting difficulties > mentioned by George. > > Regards, > > Henry > > On Thu, 26 Oct 2006 23:02:00 EDT FrankReedCT@aol.com writes: >> Henry H you wrote: >> "If the truth were to be known, the conventional wisdom of my day >> was to >> leave the sextant alone, crud and all. The more encrusted a >> sailor's >> sextant might be, the more experienced he (no shes then) and >> competent he >> was thought to be. The cigarette/cigar ash polish was advanced as >> an >> alternative for the fastidious to use. How times have changed!" >> >> Can you describe this process of polishing with ashes? I'm having a >> hard >> time picturing it. Are you pouring ashes onto the arc and then >> rubbing them with >> your finger, or do you rub the cigarette/cigar itself, ashen end >> down, along >> the arc? >> >> -FER >> 42.0N 87.7W, or 41.4N 72.1W. >> www.HistoricalAtlas.com/lunars >> >> >> > > > --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To unsubscribe, send email to NavListemail@example.com -~----------~----~----~----~------~----~------~--~---