Hg spectrum of a 15 ft Rowland grating of 1895 - Page 1
Forum section: electronics / general

author: Physikfan
author_rank: Regular Contributor
timestamp: March 15, 2019, 05:26:28 pm
content: The spectrum is a Hg spectrum of a 15 ft Rowland grating of 1895, photographed with a Nikon D3, f = 200 mm.Rowland gratingHg spectrumSpectrum calculated from the photo

author: coppercone2
author_rank: Super Contributor
timestamp: March 15, 2019, 11:46:56 pm
content: why is it so dirty? someone should clean thatis there another picture of a maintained/new one?

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: March 18, 2019, 03:26:22 am
content: Hi,Nice!Is the actual grating the 11X4 CM size?Cheers,Corby

author: Physikfan
author_rank: Regular Contributor
timestamp: March 18, 2019, 02:34:18 pm
content: The grating is 124 years old, intensive cleaning may cause some damage.The grating is 108 mm x 45 mm.

author: coppercone2
author_rank: Super Contributor
timestamp: March 18, 2019, 08:00:44 pm
content: i think you need to take a better picture or encourage them to clean it. I want to see it clean very badly.

author: rhb
author_rank: Super Contributor
timestamp: March 18, 2019, 09:52:55 pm
content: The biggest issue is it's not meant to be used in the manner in which it is displayed. Much of the "dirt" is room reflections. Attempting to clean it would be a *really bad* idea.If you want to see a clean grating make one. In 1948 Scientific American had several long articles on the ruling engine John strong was building at Johns Hopkins. One short article described how amateurs had destroyed their mental health and finances trying to build ruling engines and including a caution "d not try this at home".In 1958 The Amateur Scientist column described a ruling engine built as a hobby project in the UK. It used a cadmium lamp interferometer to position the sled. Because stick slip was random, it did not have the "Rowland's ghosts" caused by periodic errors in the line spacing caused by screw errors.

author: Physikfan
author_rank: Regular Contributor
timestamp: March 18, 2019, 10:04:17 pm
content: Before trying to clean the grating you should look at the quality of the calculated spectrum

author: rhb
author_rank: Super Contributor
timestamp: March 18, 2019, 11:23:40 pm
content: Did you calculate the spectrum from the posted photo? If so, I'm *extremely* impressed and would *really* appreciate an explanation.I have 37 years of DSP (seismic processing) experience and I can't think of how I could do that with that image as input. That rarely ever happens.But it is really nice to see it. And it would be even more fun to learn something new.

author: coppercone2
author_rank: Super Contributor
timestamp: March 19, 2019, 03:12:53 am
content: I just think its extremely visually distracting to have what looks like tarnish on it.

author: Physikfan
author_rank: Regular Contributor
timestamp: March 19, 2019, 05:52:47 pm
content: Another picture of this Rowland grating:

author: coppercone2
author_rank: Super Contributor
timestamp: March 23, 2019, 03:30:53 am
content: maybe its not complicated enough to warrent a series (no idea) but it would be interesting to see a copy made then, if it can't be cleaned. like clicksprings Greek mechanism.

author: rhb
author_rank: Super Contributor
timestamp: March 23, 2019, 01:42:45 pm
content: Quote from: coppercone2 on March 23, 2019, 03:30:53 amDo you have *any* concept at all of how hard it is to make a grating? The purely mechanical engine that John Strong built in the late 40's was submersed in a large, temperature controlled oil bath. The positioning screws had measured errors of less than a millionth of an inch.The temperature in the *room* where the ruling engine is located must be controlled to 0.01 F. A human being standing in the room for a few minutes will raise the temperature 0.1 F. The machine had to be run for many hours without scribing to bring all the parts to thermal equilibrium before starting to rule a grating which took 56 hours.Nobel prize winner, A.A. Michelson, spent 8 years on his second attempt at building a ruling engine and was able to produce a good 6" grating of 110,000 lines per inch. He spent 6 years on his first attempt. The 2nd machine was intended to make 12" gratings but appears never to have been able to make a grating that large.

author: guenthert
author_rank: Frequent Contributor
timestamp: March 23, 2019, 08:53:23 pm
content: So the grating displayed above is rather 15"  long, not 15' ? I was wondering whether that number would refer to the linear dimension.

author: coppercone2
author_rank: Super Contributor
timestamp: March 23, 2019, 09:01:16 pm
content: Quote from: rhb on March 23, 2019, 01:42:45 pmyea its a bit more interesting then the antikyra mechanism, whats your point? im saying it would be a good project. maybe some rich guy can do it.

author: rhb
author_rank: Super Contributor
timestamp: March 23, 2019, 09:20:33 pm
content: See my previous post on the 1958 hobby build.

author: coppercone2
author_rank: Super Contributor
timestamp: March 23, 2019, 09:24:10 pm
content: its not on youtube

author: tomato
author_rank: Regular Contributor
timestamp: March 24, 2019, 02:04:09 am
content: Quote from: guenthert on March 23, 2019, 08:53:23 pmHe stated the grating measured 108 mm x 45 mm. It could have been used in spectrometer that was 15 ft long.

author: Physikfan
author_rank: Regular Contributor
timestamp: March 24, 2019, 11:38:23 am
content: Ad rhb:"Did you calculate the spectrum from the posted photo? If so, I'm *extremely* impressed and would *really* appreciate an explanation.But it is really nice to see it. And it would be even more fun to learn something new."The software used for calculating a spectrum from a photo:https://www.rspec-astro.com/https://www.rspec-astro.com/features/https://www.rspec-astro.com/getting-started-pdf/https://www.rspec-astro.com/setupdownload/https://www.rspec-astro.com/download/Getting%20Started%20in%20Astronomical%20Spectroscopy%20using%20RSpec.pdf

author: Physikfan
author_rank: Regular Contributor
timestamp: March 24, 2019, 11:55:11 am
content: Ad 5065AGuru, Corby:"Is the actual grating the 11X4 CM size?"Please, from where you got the information of the correct size of this Rowland grating, it is a real prediction?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: March 24, 2019, 02:21:17 pm
content: AFAIK, gratings are almost never cleaned because damage is certain. The Richardson Grating Lab is here in Rochester NY, but I can't find any good photos of the engine(s). Almost all the good history is locked up behind the OSA paywall, a sad state of affairs.http://obswww.unige.ch/~pepe/Repository/RGL_Grating_Handbook.pdf

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: March 24, 2019, 03:56:00 pm
content: Physikfan,I found that size when searching Rowland gratings on the web.Tried again this morning but can't find it again.I believe that the 15 foot refers to the radius of curvature of the blank.By the way trying to replicate this grating is at least as hard or more than trying to manufacture a Hydrogen Maser at home! NOT an easy feat!Cheers,Corby

author: Physikfan
author_rank: Regular Contributor
timestamp: March 24, 2019, 05:11:24 pm
content: Hi Corby"I believe that the 15 foot refers to the radius of curvature of the blank."This is true, 15 ft is also the diameter of the Rowland circle.