552 



NA TURE 



^October 6. 1892 



Nova Auriga. — In some further notes that we have re- 

 ferring to the brightness and the spectrum of the Nova, we find 

 that most observers estimate the star's magnitude to lie between 

 10 and 10.5. Herr Belopolsky, who has examined the star 

 spectroscopically, has been able to see one or two lines ; a later 

 estimation of the brightest gave a wave-length of 501, while the 

 second line proved too variable in brightness to allow of a 

 sufficiently correct measurement. 



To Astronomiscke Nachrkhten, l>io. -^ll?,, Mr. H. Seelinger 

 contributes a very important article, in which he suggests an 

 hypothesis which may be said to approach that put forward by 

 Mr. Lockyer some time ago. He assumes (and a very fair 

 assumption too) that the cosmos contains innumerable more or 

 less elongated forms of very thin and small particles, and that 

 the Nova was produced by a body rushing into one of these, 

 so to speak, clouds. On entering this cosmical cloud, at once 

 there would be a condition for producing heat, and therefore 

 light, and we have only to imagine the cloud to be of varying 

 thicknesses to account for the peculiar fluctuations which attended 

 the light of the Nova. That such a case should take place seems 

 in itself more probable than that of two bodies passing very near 

 one another, and we already know that such streams as suggested 

 do exist. Our November shower, for instance, is such a swarm, 

 only on a scale very much smaller than that inferred above. 



GEOGRAPHICAL NOTES. 



Until recently the Samoan calendar corresponded with the 

 Australian, but on July 4 last a change was made by order of 

 King Malietoa. Tuesday, July 5, was reckoned a second time 

 as Monday, July 4, thereby coming into harmony with the 

 American and European reckoning. Samoa, lying to the east of 

 180°, had retained the old system of time, superseded by the 

 general acceptance of that meridian as the line at which the 

 date is rectified by vessels at sea. 



Captain Lugard reached London from Uganda on Sun- 

 day night. It is gratifying to know that his three years' resi- 

 dence in equatorial Africa, and the severe strain of recent 

 events, have not told adversely on his health. He will prob- 

 ably communicate the important geographical results obtained 

 by him to a special meeting of the Royal Geographical Society 

 in November. 



The arrangements for the new session of the Royal Geo- 

 graphical Society present several new features. In addition to 

 the ordinary meetings it is proposed to give a special series of 

 Christmas lectures to young people ; to be followed fortnightly 

 by a course of ten education lectures, specially adapted for 

 teachers, by Mr. H. J. Mackinder. The ordinary meetings as 

 provisionally arranged begin on November 14 by a paper on his 

 proposed North Polar exiedition by Dr. Nansen. Mr. Joseph 

 Thomson will follow with an account of his expedition to Lake 

 Bangweolo. Captain Bower will describe his journey across 

 Tibet, and Captain Lugard will recount his discoveries in equa- 

 torial Africa. Prof. Milne and Mr. Savage Landor have 

 promised papers on Yesso, Major Rundell on the Siyin Chins, I 

 Mr. H. O. Forbes on the Chatham Islands, and Captain 

 Gallwey on Benin. It is hoped that Mr. Conway will return 

 to describe his adventures in the Karakoram mountains. Apart 

 from the records of travel to which the attention af the Society 

 in its ordinary meetings has usually been mainly devoted, there 

 will be papers dealing with the more general and scientific 

 aspects of Geography. The Prince of Monaco will probably 

 describe his experiments on the Atlantic currents. Sir Archibald ' 

 Geikie will lecture on types of scenery, Prof. Bonney on the I 

 work of glaciers, Mr. J. Y. Buchanan on the windings of ] 

 rivers, and Dr. Schlichter on his new photographic method of I 

 determining longitude. 



The last number of Petennamt's Mitteilungen contains an 

 important paper by Dr. Alois Bludau giving the co-ordinates 

 for Lambert's equivalent area azimuthal projection of the map 

 of Africa. An outline of the continent on this projection, 

 the central point of which is on the equator in 20° E. long., 

 shows the remarkable suitability of the map for representing 

 Africa, the distortion being inappreciable, 



NO. 1197, VOL. 46] 



MAGNETIC INDUCTION} 



'TPHE lecturer remarked that it was no less than forty-five years 

 ■*■ since the magnetic properties of materials had formed the 

 subject of an evening discourse before the British Association. 

 At the Oxford meeting in 1847 the lecturer was Michael 

 Faraday, who had only a little while before made his great dis- 

 covery of diamagnetism and been led to the splendid generaliza- 

 tion that all substances are in one way or other, and in greater 

 or less degree, susceptible of magnetic influence. And it was 

 an interesting coincidence that in the same year, partly indeed 

 at that same Oxford meeting of the Association, the foundation 

 of the modern mathematical treatment of magnetism had been 

 laid by that infant phenomenon, whom in the vigour of his 

 maturity we were now learning to call Lord Kelvin. Discard- 

 ing the arbitrary hypotheses of earlier theoretical writers, Lord 

 Kelvin, then a stripling at Cambridge, had proceeded to give 

 mathematical expression to the observations and intuitions of 

 Faraday. In recent years the science of magnetism had 

 advanced fast, keeping pace with the advance of its industrial 

 applications. In common with other branches of electricity it 

 had discovered the advantage of being useful. The debt which 

 practice owed to science had been repaid with interest. In 

 other departments of science it might be true that there were de- 

 votees whose chief pride in their work lay in their reflection that 

 it could never be of any use to anybody : this temper of mind 

 was not possible to an electrician. The language of electricians 

 had passed with bewildering rapidity into Acts of Parliament and 

 provisional orders of the Board of Trade, and the demands of 

 industry had stim'ulated discovery and fostered exactness in 

 measurement. It was the beneficent reaction of practice on 

 science that had enabled the great work of the Electrical 

 Standards Committee of the British Association to be brought 

 to a successful issue. As a fruit of that work electricians were 

 in high hope that this Edinburgh meeting would result in an in- 

 ternational agreement with regard to the electrical units, so that 

 whatever the Great Powers might find to differ about they would 

 at least be of one mind as to the magnitude of the volt, the 

 ampere, and the ohm. In the co-operation of Prof, von Helm- 

 holtz on the part of Germany, and of M. Mascart on the part 

 of France, with Lords Kelvin and Rayleigh and their English 

 colleagues, there were surely the elements of a Triple Alliance 

 which should secure to the electrical world peace, not only with 

 honour, but with precision. 



The lecture of Faraday in 1847 had dealt with the condition 

 induced by magnetic force in matter which was not ordinarily 

 magnetic. Substances were broadly divisible into two classes, 

 those which were strongly susceptible to magnetic influence and 

 those that were only very feebly susceptible. The latter was by 

 far the most numerous class, and it was with it that Faraday 

 dealt in his lecture. The strongly magnetic substances were 

 iron and its various derivatives, which passed by the general 

 name of steel, also nickel and cobalt. A recent discovery by Prof. 

 Dewar seemed to require that oxygen, in the liquid state, should 

 be added to this list. The lecturer proposed to confine his 

 attention to the phenomena of magnetization which were ex- 

 hibited by the strongly magnetic metals. Let any one of these 

 metals be submitted to the action of a magnetizing force such 

 as would be produced if an electric current were passed through 

 a coil of insulated wire surrounding the metal. As the current 

 was gradually increased, the magnetization passed through three 

 stages. It beqan very gradually ; at first, while the current was 

 still weak, there was but little magnetism developed. Then a 

 stage came on in which the magnetic state was acquired with 

 great rapidity ; a small increase in the current now caused an 

 enormous gain of magnetism. Finally, the process passed into 

 a third stage, when the magnetism was again acquired slowly, 

 and however much the magnetizing current was increased it was 

 found to be impossible to force the magnetism to exceed a certain 

 limiting value. This was the phenomenon of magnetic satura- 

 tion. Recent researches had given definiteness to the rather 

 vague idea which used to be expressed by this phrase, and it was 

 now known not only that a limit existed, but what its values were 

 in the several magnetic metals. The lecturer illustrated the 

 three stages in the magnetizing process by means of the lantern, 

 exhibiting curves which showed the connection between mag- 



1 Abstract of an evening lecture delivered before the British Association, 

 at Edinburgh, August 8, 1892, by J. A. Ewing, M.A., F'.R.S., Professor of 

 Mechanism and Applied Mechanics, Cambridge University. 



