224 



NATURE 



[November 22, 1917 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



On the Theory of Magneto-ionisation. 



I BEG permission to make a few remarks on the 

 note in Nature of September 13, p. 32, in which one 

 of my latest papers is criticised, the one in which 1 

 gfxve, I think, a direct proof of magneto-ionisation. 



In the experiment which the writer of the note 

 takes into consideration the intensity of the current 

 in the air ionised by a beam of X-rays between two 

 parallel metal plates is measured. I find that a mag- 

 netic field directed perpendicularly to the electric field, 

 and the intensity of which is below a certain value, 

 causes an increase of current, although the deviations 

 of the ions and electrons tend to produce a decrease. 

 This effect is uncertain in the case of small potential 

 differences, but it becomes considerable when ionisa- 

 tion by collision begins. 



The writer of the note remarked that " when a. 

 magnetic field of 430 gauss is superimposed, there is 

 found a current decrease . . ." Now, the numerical 

 table to which he alludes is not the only one given 

 in the paper, and it shows such a decrease (which is 

 very small) in one case only, which may be considered 

 as accounted for by experimental error, since nothing 

 of the kind is found in the other numerical tables. 

 That, of course, leads one to suppose that the writer 

 is not fully acquainted with certain parts of my work, 

 and what he says farther on seems to confirm this 

 supposition : " In the opinion of the writer of this note 

 Prof. Righi's interpretation of his results is by no 

 means the only one which is possible, and though his 

 ingenious experiments are of great interest, his theory 

 will need further support before it obtains general 

 acceptance. In particular, it will be necessary to show 

 that the increase of current is not caused by the 

 oblique, and therefore longer, paths of the ions under 

 the joint actions of the two fields." 



The writer then offers a new theory, or, more 

 exactly, he states a general idea, which he seems to 

 consider to be preferable to my theory. But this idea 

 cannot be admitted, as I now propose to show. 



Apart from the fact that the writer appears to 

 believe that the effect of the magnetic field is simply 

 the obhquity of the trajectory of the ions, whereas 

 these trajectories become certain well-known curves 

 (which may be deduced from the formulae given in 

 the third paragraph of the note added to my paper), 

 I at once make the fundamental objection that it is 

 not sufficient to increase the distance travelled over by 

 an ion in order that the latter may become capable 

 of ionising a larger number of atoms. In fact, as in 

 ionisation by collision an ion loses a part of its kinetic 

 energy, it would be necessary to prove that the mag- 

 netic field causes the said energv to increase. Now 

 this is not at all the case, since by means of the 

 formulae of the movement of an ion in an electric and 

 magnetic field it is demonstrated that when the ion 

 traverses a plane perpendicular to the electric field it 

 possesses exactly the same velocity, be the magnetic 

 field existent or not. 



It may be added that when the magnetic field does 

 exist, the speed of the ion mav increase only to a 

 maximum value, after which it decreases again, the 

 Ion retroceding in respect of the lines of electric force, 

 while if the magnetic field does not exist, the velocity 

 may increase without limit, provided it be not stopped 

 by the electrode which attracts it or by collision with 



NO. 2508, VOL. 100] 



molecules. All this is clearly understood when one 

 knows that, apart from the velocity parallel to the 

 magnetic force, which remains constant, the trajectory 

 of the ion is nothing but the curve described by a 

 point travelling at a constant speed over a circumfer- 

 ence, while the latter is itself travelling uniformly in 

 a straight line in a direction perpendicular to the two 

 fields. 



Finally, I wish to point out that, even if the idea 

 expressed by the writer of the note did not lack a 

 basis, my theory 'could not easily be rejected. It is» 

 in fact, but a direct consequence of the conceptions 

 already accepted by most physicists, nor does it need 

 the addition of any subsidiary hypothesis. 



As a matter of fact, it being admitted that atoms, 

 have satellite electrons, they must tend to orient them- 

 selves in the magnetic field as if the orbits of such 

 electrons were closed electric currents. Now the sense 

 of this orientation is such that the force due to the 

 field, and acting on the electrons, is directed towards 

 the outside of the orbits, which causes a decrease of 

 the energy required to detach them from the rest of 

 the atoms. 



It is this facility of ionisation produced by the mag- 

 netic field that constitutes "magneto-ionisation." 



AUGUSTO RiGHI. 



Bologna (Italy), September 27. 



I AM sorry if, owing perhaps to the brevity of my 

 note, I have led Prof. Righi to think that, in my 

 opinion, his theory of magneto-ionisation can be 

 "easily rejected." Nothing was further from my in- 

 tention. I believe I have read all Prof. Righi's papers 

 on the subject as they have appeared, and have re- 

 peated some of his experiments. The impression they 

 have left on my mind is that, although Prof. Righi's 

 theory gives a plausible explanation of the complex 

 phenomena investigated, yet it is not the only one 

 possible, and further work is necessary before a final 

 conclusion can be reached. I did not express a prefer- 

 ence for another theory. I merely suggested objec- 

 tions that would have to be met before the theory 

 under discussion could be unhesitatingly accepted. 

 The question as to whether I have given a fair account 

 of the numerical results must be left to the decision 

 of the readers of the memoir. 



The Writer of the Note. 



The Introduction of the Word "Magneton." 



The word "magneton" is now so frequently used 

 that it has seemed worth while to me to seek to learn 

 to whom is due this addition to the vocabulary of 

 physics. 



So far as I can find. Dr. L. A. Bauer was the first to 

 employ the word. In the weekly journal. Science 

 (June 10, 19 10, vol. xxxi., p. 920), is a report of a 

 meeting of the Philosophical Society of Washington, 

 D.C., held on May 7, 1910. There is included an 

 abstract of a paper by Dr. Bauer entitled " Is there 

 an Emanation from a Magnetised Substance?" in 

 which the following occurs: — "The corpuscles in 

 magnetism might be atomic systems in which the elec- 

 tron is revolving about an inner nucleus consisHng, for 

 example, of a positive ion, such as assumed by Righi 

 for the formation of his so-called 'magnetic rays.' . . . 

 Since the system creates an atomic magnetic field the 

 axis of which passes through the centre of rotation 

 of the electron and perpendicular to the plane of rota- 

 tion, the speaker suggested calling such systems ' mag- 

 netons.'" 



In a letter to me Dr. Bauer says : — "The term was 

 used not only in my paper before the Philosophical 

 Society of Washington on May 7, 1910, but also in my 



