Septemeek 5, 1907] 



NATURE 



481 



on May 6, in all 9s fairs which are strictly May 6 fairs; 

 add 56 to the 53 on August 5, and regard them all as 

 strictly August 8 fairs ; and add 79 to the 43 on 

 November 8, though there are more fairs in October claim- 

 ing such recognition. 



Our lowest possible estimate of true May-year fairs is 

 now as follows :■ — 



Total 1074 

 ., 362 



Feb. May Aug. Nov. 



77 ... 416 ... 261 ... 321 

 Astronomical 35 ... 96 ... 109 .. 122 

 The table of the quarter-day groups must likewise be 

 corrected, only to strengthen materially the whole case for 

 the May-year. (Only in a few cases have I been able to 

 correct Owen's spelling of place-names.) 



/I\ 



The Bardic Mystic Sign. (Reproduced from " Barddas." " Morien " quotes 

 Payne Knight's "Symbolical Language of Art and Mythology," pp. 

 69, 70, where it is stated that the same sign, with a small circle or 

 riogat the converging point of the three lines, is a very ancient emblem 

 in Asia Minor. The angles in Knight's sketch, as reproduced by 

 *' Morien," are also exactly 28' each.) 



George Meredith makes one of his Welsh characters 

 "think in triads." Here is a new triad: — "The three 

 interpreters of the riddle of the stones : the Sun, the 

 Gorsedd, and the Popular Fair." I have already shown 

 (N.1TURE, May 2) that the May year is the true basis of 

 the Gorsedd. The bardic .Yod Cyvrin, Mystic Sign, which 

 Mr. A. L. Lewis (Nature, June 6) associates very 

 naturally with the " broad arrow," is really a miniature 

 Gorsedd. I have tested several printed cuts of the sign 

 and find the angles to be 28", that is, regarding the middle 

 line as an east-west line, the right line points to N. 62° E. 

 and the left to S. 62° E., the only possible emblematic 

 representation, in the simplest form, of the May year in 

 the Gorsedd country. John Griffith. 



KATHODE RAYS AND THE AURORA} 



'X'HE idea that kathode rays play a part in aurora has 

 been advanced by several physicists. Prof. Kr. Birke- 

 land (" Expedition Norvegienne," 1899-1900, Christiania, 

 1901) has described a number of phenomena produced by 

 kathode rays in the neighbourhood of a magnetised sphere, 

 which resemble various types of aurora. He supposed the 

 sun to be a primary source for kathode rays, w-hich might 

 set up secondary rays in the earth's atmosphere. Mr. C. 

 Stormer has carried out elaborate calculations as to the 

 possible ways in which electrified particles coming from a 

 great distance can approach a magnetised "earth"; his 



results tend to limit the approaching particles to the space 

 near the magnetic poles. Prof. S. Arrhenius has suppos<d 

 electrified particles to be driven from the sun by the repul- 

 sion of light and to reach the ear'.h's atmosphere in about 

 two days, originating aurora and magnetic storms. 



M. Villard refers to .\rrhenius's theory, but seems some- 

 what sceptical as to the supposed solar origin of the elec- 

 trified particles. His own views appear to be a combination 

 of theory and observation as to what happens to ions or 

 electrified bodies of any kind moving in a magnetic field. 

 In a uniform field the ion, when travelling with uniform 

 velocity, describes a regular helijc on a cylinder the a.\is of 



' "Les Rayons cathodiques et lAurore boreale." By M. P. Villard. 

 (.Bulletin di la Societe d' Etuourageiitenl potir t' Induitrie ruitionaU, May. 

 1907.) 



which is parallel to the lines of magnetic force. The radius of 

 the cylinder varies directly as the component of the velocity 

 perpendicular to the lines of magnetic force, and inversely 

 as the intensity of the lield. Suppose, however, that the 

 magnetic field is not uniform, but increases in intensity in 

 the direction in which llie ion travels ; then, as has been 

 shown by Poincar^, the path forms a curve with diminish- 

 ing spirals on a cone, and before actually reaching the 

 summit of the cone the particle ceases to advance, and 

 retires, the spirals gradually opening out. If, for instance, 

 the field is that due to two elongated parallel poles, then if 

 the particle gets under weigh between the poles, travelling 

 obliquely to the lines of force, there is a regular game of 

 battledore and shuttlecock, the particle zigzagging to and 

 fro slantwise, reversing its direction whenever it gets 

 within a certain distance of either pole. 



-M. \illard supposes ions to get in motion somewhere in the 

 earth's atmosphere. As to e.\actly how this comes about 

 he is not prepared to dogmatise. Ho is inclined to think 

 that cirrus clouds — which he believes to consist of ice 

 panicles negatively electrified —under the influence of ultra- 

 violet light, or less probably under a solar bombardment 

 such as .Arrhenius postulates, are probable sources. He also 

 thinks that not improbably a part is played by cosmical 

 dust encountered in the earth's movement through space. 

 Ions starting, say, from a cirrus cloud, and moving 

 obliquely to the lines of magnetic force in the earth's atmo- 

 sphere, will travel each in a spiral, the whole together 

 forming a sort of luminous spindle, which on getting within 

 a certain distance of, say, the south magnetic pole, turns 

 as if reflected, makes for the north pole, suffers a second 

 reflection there, and so on. Eig. 1, copied from .M. Vil- 

 lard 's paper, represents the idea diagrammatically. The 

 particles are supposed 10 come in at the top (answering to 

 the west) and first to lrav_-l south. The movement may 

 be supposed to be set up by ultra-violet light from the sun 

 falling on cirrus. The first band or two will thus be in the 

 >.iill illuminated hemisphere, and so invisible ; succeeding 

 bands will be overhead in the unlightcd hemisphere, and 

 will be visible. Passing further to the east, the energy will 

 be gradually dissipated and the aurora cease to be visible, 

 thus explaining why the late evening, and not the morning, 

 is normally the time of most brilliant aurora. 



To fit the theory, the charge carried by the particles must 

 be negative. If it were positive, the motion would be 

 from the east, and the principal aurora would be in the 

 early morning. Eig. 2 reproduces a photograph showing 

 the actual appearance near a magnetic pole from one point 

 of view, in one of -M. Villard's e.xperiments. He regards 

 the intensifications of brightness, due to the superposition 



NO. 1975, VOL. 76] 



of the direct and return paths, as answering to an auroral 

 arc. Below the arc there would, he says, be total dark- 

 ness — answering to the " dark segment " of the ordinary 

 aurora — but for a special form of discharge which he 

 terms " magneto-kathodic " rays ; these rays require, he 

 says, a very steep potential gradient, and do not exist in 

 the earth's atmosphere. Changes in the magnetic field or 



