November 2, 1899] 



NATURE 



>3 



made generally known through the medium of the widely 

 circulated journal Nature, for on November 19, 1897, I 

 sent photographic negatives to the office of Nature for 

 reproduction in that journal. These negatives showed 

 the quartets as well as the pure sharp triplets and the 

 ■diffuse triplets ^ which occur in the spectra of cadmium 

 and zinc. They were produced by me in the end of 

 October 1897, and were, I believe, the first photographic 

 record of the actual magnetic tripling and quadrupling of 

 the spectral lines. These negatives, however, were not 

 considered suitable for reproduction in N.\ture (see 

 letter to Nature, p. 173, December 23, 1897), but were 

 subsequently enlarged and reproduced with great clear- 

 ness in the Philosophical Magazine (April 1898). 



In my letter to NATURE accompanying the negatives I 

 did not dwell on the quartet form, as I did not wish to 

 commit myself, or persuade others, to the belief that the 

 quartet was really a magnetic quartet, i.e. produced ex- 

 clusively by the magnetic field. It was quite open to 

 ■belief at that time that the quartet form might be pro- 

 duced from the triplet by other mechanical causes, for 

 ■example by reversal of the central line of the triplet, or 

 in other ways, as noticed in my paper mentioned above. 

 After prolonged effort I proved beyond all doubt that 

 these variations of the triplet type (the quartet, &c.) are 

 ■true magnetic perturbations, and are not due to any 

 ■other cause ; but this required to be proved, and for this 

 purpose a very strong magnetic field was necessary. 



With this field I found, as already announced in 

 Nature, that the quartet form becomes resolved into a 

 sextet by the splitting up of the side lines into doublets. 

 It is, therefore, not really a quartet after all, but a sextet. 



With regard to other points, namely, the fact that the 

 magnetic effect does not conform to the law deduced by 

 the simple theory (viz. that 5 X oc X^), and the surmise 

 that some such law might hold for groups of lines, a 

 reference to my first paper, already mentioned ( Trans. 

 Roy. Dub. Sac, December 22, 1897), will show both 

 these points clearly emphasised there. On p. 387 I 

 ■state that while some lines were converted into triplets 

 ■'' others photograph as doublets, or weak middled, 

 greatly broadened lines, having the appearance of 

 •quartets ; while on the other hand many lines appear 

 to be simply broadened in the same magnetic field, and 

 •others seem to be scarcely influenced in the same magnetic 

 4eld." Thus the effect appeared to be lawless for the 

 spectral lines taken as a whole in any one substance ; 

 but I go on to say t^'t "pt^jhaps it might be possible to 

 •group the spectral lines bt e3v.I: substance into sets, so 

 that some law of wave-length might apply to the lines of 

 •each set." 



At this early date I was already seeking for some such 

 law, and I had before the close of 1897 proved that the 

 law, whatever it might be, was not the same as that 

 which governs the pressural shift of the spectral lines 

 studied by Messrs. Humphreys and Mohler (see Proc. 

 Roy. Soc. of London, January 1898). 



My search has resulted in the discovery of a general 

 law which has so far proved to be in complete agreement 

 •with all the observed facts. 



With regard to the spectrum of iron, you will observe 

 in my note in the Proc. Roy. Soc, January 1898, that I 

 was at that early date of opinion that the spectrum of 

 iron exhibited no peculiarities of its own in the magnetic 

 field. I examined iron early because I thought that by 

 reason of its magnetic properties its spectral lines 

 jnight show some decided peculiarities (but iron is not 

 magnetic above 700' C, therefore my hopes were not 

 very decided). On the whole I still adhere to that 

 •opinion, for although the spectral lines of iron show a 

 variety of effect, yet these effects are the same in 

 character or in kind as those which are observed in 

 other substances. This and other matters I have 



1 Really noaets as subsequently determined. 



NO. 1566, VOL. 61] 



already treated of fully elsewhere (Phil. Mag. and 

 Nature). 



The accompanying iUustrations (Figs. I, 2, 3) have 

 been reproduced from the plate given in the memoir 

 read before the Royal Dublin Society on December 22, 

 1897. They show that the quartets were observed and 

 photographed by the author certainly before that date. 

 Thomas Preston. 



NOTES. 



Dr. Janssen, director of the Meudon Observatory, has issued 

 a circular in which he announces that the success of last year's 

 observations of the Leonid meteors from a balloon has led to 

 arrangements being made to repeat the experiment during the 

 forthcoming shower. Last year, a number of these meteors were 

 observed from a balloon above Paris, though the city itself was at 

 the time enveloped in a thick fog. It is important that numerous 

 observations of the Leonid meteors should be made from as 

 many places as possible ; and as balloons render observers inde- 

 pendent of cloudy skies, they are evidently of great advantage 

 upon occasions such as that to which astronomers are looking 

 forward. We are informed that two balloon ascents are to take 

 place near St. Denis. The first ascent will be made on the 

 night of November 14-15, with the Aerostat, and the second, 

 on the following night, with the Centaure. Two seats in 

 each balloon will be at the disposal of Dr. Janssen, who will 

 nominate observers to occupy them, without distinction of 

 nationality. The names of the observers will be announced at 

 the next meeting 01 the French Astronomical Society, on 

 November 8. 



The opening meeting of the new session of tfie Institution or 

 Electrical Engineers will take place on Thursday, November 16, 

 when the premiums awarded for papers read or published 

 during the session 1898-99 will be presented, and the president. 

 Prof. Silvanus P. Thompson, F.R.S., will deliver his inaugural 

 address. 



A SERIES of monthly lantern lectures has been arranged by 

 the Royal Photographic Society. The first lecture will take 

 place on Tuesday, November 7, when Mr. J. J. Vezey 

 will describe "Some Medioeval Towns of Germany," illustrated 

 with slides by Commander C. E. Gladstone, R.N. 



The death of Mr. Grant Allen, at the age of fifty-on « re. 

 moves one of the most popular of scientific authors whose 

 writings have induced many readers to watch the workings of 

 animate nature. His first scientific work, on "Physiological 

 Aesthetics," was published in 1877, and was foil'^-yed, in 

 chronological order, by "The Colour Sense," * '^i> /-^"-volu- 

 tionist at Large," "Vignettes from Nature," "CoivsS'rs of 

 Flowers," "Colin Clout's Calendar," "Flowers and their 

 Pedigrees," "Charles Darwin," "Science in Arcady," "The 

 Evolution of the Idea of God," &c. In addition, Mr. Allen 

 contributed numerous articles on natural history topics to 

 periodical literature. All his scientific articles and books are 

 attractively composed, and they have been the means of impart- 

 ing much popular instruction to general readers. 



Among the privileges which the Hampstead Astronomical 

 and Scientific Society is able to offer its members is the use of 

 a reflecting telescope of loj-inch mirror, which is erected in a 

 small observatory on the East Heath, by permission of the 

 London County Council. Interest in practical astronomy is 

 aroused by this means, and the instructive lectures given at the 

 meetings of the Society direct attention to facts and things 

 terrestrial as well as celestial. A course of five lectures on 

 astronomy will be given by Mr. P. E. Vizard in connection 

 with the Society on Monday evenings, commencing on 

 November 20. Mr. Vizard will also lecture on November 10, 



