Here’s a little obscure physics trivia for you: who first suggested that an atom might have a structure consisting of a positively-charged “nucleus” surrounded by orbiting electrons?
The easy, and mostly correct, answer is Ernest Rutherford. In 1909, he supervised two of his students (Geiger and Marsden) in an experiment to probe the structure of atoms using alpha-particles. Surprisingly, they found that occasionally one of the alpha-particles would be almost completely reflected from their sample, which should not have happened according to the Thomson “plum-pudding” model of the era. Rutherford himself later remarked, “It was almost as incredible as if you fired a fifteen-inch shell at a piece of tissue paper and it came back and hit you.” In 1911, Rutherford published a paper (“The Scattering of Alpha and Beta Particles by Matter and the Structure of the Atom,” Phil Mag, ser 6, 21 (1911), 669-88) in which he argued that the results suggested that the atom consisted of electrons orbiting a very small, dense, positively-charged nucleus which contained most of the atom’s mass. This realization was a major breakthrough in atomic physics and eventually led to our modern picture of atomic structure.
When I was working on my post on “failed atomic models” some time ago, however, I encountered an off-hand remark that Jean Baptiste Perrin, another giant in atomic theory, had first proposed a nucleo-planetary atomic model in 1901. Curiously, though, I was unable to find a reference to it, and I’ve always wondered why.
Perrin’s own Nobel lecture of 1926 provides most of the answer:
I was, I believe, the first to assume that the atom had a structure reminding to that of the solar system where the “planetary” electrons circulate around a positive “Sun”, the attraction by the centre being counterbalanced by the force of inertia (1901). But I never tried or even saw any means of verifying this conception. Rutherford (who had doubtless arrived at it independently, but who also had the delicacy to refer to the short phrase dropped during a lecture in which I had stated it) understood that the essential difference between his conception and that of J.J. Thomson was that there existed near the positive and quasi-punctual Sun, enormous electrical fields as compared with those which would exist inside or outside a homogeneous positive sphere having the same charge, but embracing the whole atom.
In other words, Perrin first proposed the nucleo-planetary model, but never pursued the idea beyond some basic speculations. Rutherford is rightly given most of the credit for the development of the model, as he supervised the experiments which led to its verification and worked out the rigorous theory behind it.
One thing I would like to find, though, is the place where Rutherford referred to Perrin’s planetary model! I’ve been searching through Rutherford’s papers on the nuclear model, but so far have not found any reference to Perrin. If I find it, I’ll write an additional post on the subject…
Skulls in the Stars 
The book “The periodic table” by Eric R. Scerri (preview available on Google Books) cites Perrin’s views in the year 1901:
“Each atom will consist of one or more highly charged positive bodies, akind of positive sun whose charge is much higher than that of a corpuscule (electron), and also of a kind of small negative planets, all these bodies gravitating under the action of electrical forces, and with total negative charge exactly equal to the total positive charge, so that the atom electrically neutral.”
Further along the way the book states:
“In 1903, Hantaro Nagaoka in Japan independently proposed a Saturnian atom in which electrons move in one or more rings around a central body. A translation of one of his lectures was published in 1904 in the Philosophical Magazine and was subsequently quoted by leading physicists such as Ernest Rutherford and Henri Poincaré”
So it seems that Perrin’s idea of a planetary atom was shared by Nagaoka whose translated works from Japanese to English came to the eyes of Rutherford before the translation of Perrin’s own work on this topic from French to English…
For a brief history on Perrin’s research on atoms and Brownian motion:
http://dx.doi.org/10.1016/j.shpsa.2008.06.003
Thank you for citing my book on the periodic table on the subject of Perrin, Nagaoka, Rutherford and the nuclear atom.
This is quite a coincidence since I was covering this material with an honors collegium class in history and philosophy of science here at UCLA just a couple of hours ago.
As I read through my chapter the following question occurred to me.
When JJ Thomson criticized the models of Perrin and Nagaoka he claimed that such solar system models would be unstable. In doing so he put forward his famous plum pudding model. But then Rutherford rehabilitated the solar system model, while modifying it with the very small central nucleus etc. But why was Rutherford unconcerned about the instability that Thomson had previously pointed out and which would eventually spell the end of the Rutherford model at the hands of Bohr?
I suppose I should go back to the articles but perhaps somebody can clear this up more quickly.
Incidentally, I have another book due to appear soon, “Selected Papers on the Periodic Table”, Imperial College Press, London.
The already published book referred to in the previous blog is at
http://www.oup.com/us/catalog/general/subject/Chemistry/?view=usa&ci=97801953
05739
regards,
eric scerri
Eric,
Thanks for the comment! I’ll have to give both of your books a look in the near future.
I have (many of) Rutherford’s papers lying around and I’ll take a look and see if he addresses the instability question.
Eric: A short & quick answer:
In Rutherford’s 1911 paper where he first proposes the nucleus, he says: “The question of the stability of the atom proposed need not be considered at this stage, for this will obviously depend upon the minute structure of the atom, and on the motion of the constituent charged parts.”
It seems on first glance that Rutherford ‘punted’ the stability question on the grounds that he had hard evidence that the nucleus existed, stability be damned! Bohr’s model may have come along so quickly that nobody had any time to look into the question in further detail. (It would be interesting, though, to hunt down if there are any papers criticizing Rutherford on those grounds.)
Thanks for looking this up. I am now also interested in seeing where Bohr addresses this issue and whether indeed he did so explicitly or whether it is one of these things that is attributed to him by all textbooks in retrospect.
Again if you have the paper(s) handy I would be interested.
I am swamped with work on another book at the moment, which I have been putting off all day.
The book is called “A tale of seven elements” and is about the last 7 elements to be discovered among the first 1-92. There are some great stories such as Professor Fred Allison from Alabama Polytechnic who insisted in dozens of publications that he was able to measure a time delay in the Faraday effect after the application of a magnetic field and that the delay was characteristic of every substance and that he was seeing elements 85 and 87. There was even an article supporting his claims in Time Magazine. It turned out to be an excellent case of what Langmuir called ‘pathological science’ in a nice article in Physics Today.
eric scerri
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