Talk:Cathode ray

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Older discussion[edit]

In /60) vessels exposed to electric field (in contemporary terms)

  • 1858 Geissler: invents pump with mercury pistons: à p~10-4
  • 1858-59 Plücker (Bonn) No glowing in the gas, but there are glowing spots on glass next to cathode… . Goldstein gives the name Cathodenstrahlen (cathode rays)
  • 1869 Plücker Rays can be deflected by magnetic filed
    • Plücker, Hittorf: Rays can be blocked by solid objects (shadows)
  • 1871 Varley: speculates cathode rays are negatively charged small bits of matter
    • Plücker: rays = molecules of cathode material? Observed thin film of platinum on glass1…
    • Crooks (English): rays = gas molecules picked up negative charge from cathode?
    • Goldstein noted that cathode rays have range of 90 cm at p=10-5, while molecules—about 1 cm. - rays cannot be molecules of any sort…
  • 1883 Hertz (Berlin): cathode rays cannot be deflected by electric filed (Now we know that the pressure was not low enough: ionized gas made E=0 inside tubes)
  • 1891 Hertz: cathode rays penetrate thin foils (like light through glass) - rays must be waves of some sort (deflectable by magnetic filed, though)
  • 1895 Perrin (French): used charge collector at the end of a glass tube to check if they have charge.- rays do have negative charge!
  • 1895 Röntgen (German): discovers X-rays (produced by cathode rays striking the glass wall…)
  • 1896 Becquerel (French): discovers radioactivity (by searching for sunlight-induced X-rays…)
  • 1897 J. J. Thomson (Professor of the Cavendish Lab at the University of Cambridge): First quantitative characteristics of rays: m/q-ratio

But can't find good hard source. Possibly useful but not available to me are:

  • Alfred Romer. "The Speculative History of Atomic Charges, 1873-1895". Isis. 33(6): 671–683.  Text " year-1942 " ignored (help)
  • Jagdish Mehra, Helmut Rechenberg (2001). The Historical Development of Quantum Theory. Springer. pp. 170–171. ISBN 0387951741.  here

There are some useful wesites:

There is so much contradictory I don't want to proceed without a good set of materials.Cutler 14:40, 22 August 2007 (UTC)

Requested move[edit]

The following discussion is an archived discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

The result of the proposal was not to move --Lox (t,c) 10:03, 9 January 2008 (UTC)

Cathode rayElectron beam — I propose this page be moved to Electron beam, because that is the more common modern name for it. "Cathode ray" is kind of antique. Electron beam currently redirects here, but electron beams are a much broader topic than things that would conventionally still be called "cathode rays". The article should use the broader and more common name. —Srleffler (talk) 05:32, 3 January 2008 (UTC)


Feel free to state your position on the renaming proposal by beginning a new line in this section with *'''Support''' or *'''Oppose''', then sign your comment with ~~~~. Since polling is not a substitute for discussion, please explain your reasons, taking into account Wikipedia's naming conventions.
  • Oppose. Agree that a little of the material on electron beams does not belong in this article, it belongs in the stub currently at electron beam technology, or perhaps in the article on charged particle beams which is was the original target of the redirect at electron beam. But cathode rays are very important historically, easily important enough to warrant an article. And probably even still important enough in current applications such as cathode ray tubes to have an article of their own. Andrewa (talk) 09:39, 5 January 2008 (UTC)
  • Oppose. Cathode rays were important in the 20th Century and are important now, and therefore merit an article. Even if these uses become obsolete, they will still warrant an article for historical reasons (in the same way as there are articles on old ships, or aircraft that are no longer in service). It would be very confusing to have to hunt through an article on all the 21st Century uses of electron beams to find the material relevant to Cathode Rays. If someone wants to write an article on broader use of electron beams, they should write such an article - but that article will be different from the one on Cathode Rays.-- (talk) 13:17, 8 January 2008 (UTC)


Any additional comments:
The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Are cathode rays visible?[edit]

A recent edit on 12:57, September 29, 2009 by User: put a "dubious" tag on the phrase "Cathode rays are invisible...", citing this site showing a homemade cathode ray tube with a glowing line in it. While interesting, this light is not the cathode rays themselves, but due to the residual air left in the tube by the simple method of creating a vacuum used in the experiment. As explained in the article, when a vacuum tube is incompletely evacuated, the cathode rays strike molecules of gas in the tube, causing them to fluoresce or glow along the beam. The matter can be settled by looking into a commercial vacuum tube in a guitar amplifier or the back of a cathode ray tube in a television set while it is operating. The only light that can be seen is the red glow of the filament. These sources 1, 2, 3 confirm that cathode rays themselves are invisible. I am removing the "dubious" tag. --ChetvornoTALK 17:32, 7 October 2009 (UTC)

As another confirmation, look at the image of the operating Maltese cross Crookes tube at the top of the article. The tube appears empty, but the glowing image of the cross on the end wall is created by the cathode rays flowing through it. --ChetvornoTALK 17:53, 7 October 2009 (UTC)
Maltese cross cathode ray demonstration tubes commonly had phosphors coating the end to make the outline of the cross more clearly visible, though the glass might glow a bit on its own, depending on the composition. Edison (talk) 19:22, 18 November 2011 (UTC)
The original Crookes tube did not have a phosphor coating and indeed relied on the glass itself glowing, which it will do quite nicely if the right glass is chosen. Soda glass works quite well glowing a blue/green colour. (talk) 16:32, 1 October 2012 (UTC)

Make Electron Beam NEW Page...[edit]

Feel free to state your position on the renaming proposal by beginning a new line in this section with *'''Support''' or *'''Oppose''', then sign your comment with ~~~~. Since polling is not a substitute for discussion, please explain your reasons, taking into account Wikipedia's naming conventions.
  • Support An electron beam is a broder topic. This is like having living organism redirect to animals, even though there are plants, monerans, protist, and fungi... WikiFanD 01:02, 6 December 2009 (UTC)....

Electron beam page[edit]

It’s a shame that modern encyclopedia redirects “electron beam” search to a historical “cathode ray” article. New (may be short, with redirections) article is needed. Electron beams now are widely used in electron microscopes, electron lithography, electron beam welding, etc.

Chivesud (talk) 19:54, 17 February 2012 (UTC)

You know what to do. Cite it and write it! --Wtshymanski (talk) 20:06, 17 February 2012 (UTC)

Diagram of Crookes tube.[edit]

A schematic diagram of a Crookes tube apparatus. A is a low voltage power supply to heat cathode C (a "cold cathode" was used by Crookes). B is a high voltage power supply to energize the anode P. Shadow mask M is connected to the cathode potential and its image is seen on the phosphor as a non-glowing area.

The diagram of the Crookes tube in the article is wholly incorrect (reproduced here). The caption readily acknowledges that Crooke used a cold cathode as opposed to a hot cathode and I can forgive this lapse because modern reproductions do tend to use hot cathodes. However the caption states that the high voltage supply is used to energise the anode 'P'. Unfortunately, the anode is missing from the illustration. The glass end was not the anode, and in any case, being glass (a non conductor) it would be pointless making an electrical connection to it. I have already removed the reference to the 'anode' being phosphor coated - it wasn't. The tube relied on the glass itself 'fluorescing' which it didn't, there was another mechanism at work but that's another story.

The maltese cross was not connected to the cathode (and indeed is not even on modern reproduction tubes). If it was then it itself would have be a source of cathode rays in the cold cathode version. I do not have the resources or skill to correct the illustration, but if anyone else wants a go, this might be a good starting point. (talk) 16:27, 1 October 2012 (UTC)

A good spot. In fact a correct diagram already exists within Wikipedia, so I have been bold and substituted it. DieSwartzPunkt (talk) 16:15, 28 February 2013 (UTC)
Yeah, great that you spotted those errors. The author was probably thinking of a standard CRT tube, which has an anode consisting of a graphite coating (aquadag) on the inner wall of the tube near the screen. --ChetvornoTALK 19:58, 28 February 2013 (UTC)

Copyright violation?[edit]

The image of the energised tube (File:Crookes-maltese-tube.jpg) which is claimed by the uploader to be his own work is, in fact, a frame grab from someone else's video. The original video can be found here. I B Wright (talk) 13:27, 1 March 2013 (UTC)

Update: I take part of it back, the You Tube video referenced above is not the original video. There are several videos on You Tube uploaded by different people showing the same sequence. I have tracked the sequence back to an instructional video on cathode rays produced by (and showing a copyright notice dated 2008 from) Universidade Federal do Rio de Janeiro (En: Federal University of Rio de Janeiro). The original vide does not seem to be available on the Internet. I B Wright (talk) 15:40, 1 March 2013 (UTC)

Discovery that Cathode Rays are an object with unique charge-to-mass ratio.[edit]

I do not want to write this myself, but a proper discussion of the "discovery" of the electron, which is a "cathode ray", should contain a number of points that presently have not been made. Most of what I know comes from some reasoning and a reading of J. J. THomson's Nobel Prize speech, rather than from a history; there might be a good history out there, of which I am unaware.

First, the fact that sharp dots of fluorescence were seen meant that most of the cathode rays were getting across undeflected; however, the vacuum was not excellent, and sometimes the cathode rays collided with the residual gas, producing electrons and ions within the tube. Second, the cathode rays were found to be deflected by an external magnetic field, in a direction consistent with a negatively charged particle (direct measurements of charge collected from the fluorescent area indicated that cathode rays were negatively charged). Third, despite efforts to obtain deflection by an external electric field, until J. J. Thomson obtained a higher vacuum, no such electrical deflection was observed.

This lack of deflection by an external electric field was due to electrical screening by the electrons and ions present within the cathode ray tube, caused by relatively infrequent (but frequent enough) collisions of the cathode rays with the residual gas in the tube. This charge within the tube is called space charge, and must have been greater than the charge on the external electric field plates. Thomson, however, produced a high enough vacuum that this space charge effect was negligible. He could then see both electric and magnetic deflection.

Thomson also must have noticed that ALL cathodes gave the same charge to mass ratio, which was much less than the charge to mass ratios obtained in electrolysis (related to Faraday's law of electrolysis). This uniqueness of the charge to mass ratio, for all cathodes, is what led cathode rays to be called a type of particle; although Thomson called them corpuscles, the next year's Nobel Prize used the word electron.

The article should also note that anodes can produce positively charged anode rays, whose charge to mass ratio is much less than for cathode rays, and which ratio varies with the type of anode.

It should also note that Thomson studied the fall of charged water droplets to estimate the charge of "cathode rays"; Millikan replaced the water droplets by non-evaporating oil droplets to obtain a more accurate value. WMSwiki (talk) 17:36, 19 April 2013 (UTC)