June 19, 1913] 



NATURE 



407 



Neptune's Faint Equatorial Belts. — Dr. T. J. J. 

 See publishes in the Astronomische Nachrichten, 

 No. 4656, a paper describing some observations he 

 made on the planet Neptune in 1899 and 1900, with 

 the 26-in. refractor of the Naval Observatory at Wash- 

 ington. On some days in those years the air was 

 particularly steady and the mottled appearance of 

 the disc of the planet accidentally attracted his atten- 

 tion. This led him more closely to scrutinise the disc, 

 and he noticed that beaded bands or belts were faintly 

 visible against the brighter body of the planet. The 

 seeing on these occasions was such that 95 Ceti, the 

 most difficult of known double stars, was resolved, 

 and other difficult pairs, such as 85 Pegasi and 

 T Cygni, measured. The bands, he says, were found 

 to be extremely faint, but on a few occasions they 

 came out with more distinctness, and he attaches 

 drawings from which their general character can be 

 inferred. Dr. See refers to Prof. Asaph Hall's ob- 

 servations with the same instrument, which gave 

 the suggestion of suspected mottlings on the 

 planet's surface, and to Prof. S. J. Brown, 

 who noticed an unsymmetrical appearance on 

 the disc. As Dr. See points out, the chief interest 

 attaching to the discovery of these equatorial belts 

 arises from the circumstance that phenomena depend- 

 ing on planetary rotation first noticed on Jupiter, 

 and then on Saturn, and finally on Uranus, are now 

 seen to be common to the most remote member of 

 the solar system. The paper concludes with a brief 

 notice of the discovery of belts on the other major 

 planets. 



Variable Stars. — Numerous recent papers deal 

 with the subject of variable stars. Prof. A. A. Nij- 

 land, of Utrecht, sends a pamphlet on the light curves 

 of twenty-three Algol stars, and the classification of 

 variables. Two papers in the Astronomische Nach- 

 richten (No. 4653, vol. cxciv.) deal respectively with 

 the ellipsoidal variables SI Tauri and S Antlia?, by 

 Harlow Shapley, and the variability of the pole star 

 by Ant. Pannekoek. 



Photometric observations of variables is the subject 

 of Padova's communication to the Mem. della Soc. dei 

 Spettroscopisti Italiani (April, disp 4a, vol. ii., ser. 2a), 

 and he deals with two Algol variables, U Ophiuchi 

 and RZ Cassiopeia; ; two variables of short period, 

 Y Ophiuchi and /3 Lyrse ; five long-period variables, 

 and two irregular variables, RS Cverni and R Scuti. 

 Light curves accompany the observations in most 

 cases. Harlow Shapley contributes a paper on the 

 visual and photographic ranges and the provisional 

 orbits of Y Piscium and RR Draconis to the April 

 number of The Astrophysical journal, while the same 

 journal also contains a second paper by Frederick H. 

 Seares on the Algol variable RR Draconis. Prof. 

 E. C. Pickering refers in Circular 177 of the Harvard 

 College Observatory to the maximum brightness of 

 Algol variables. 



KODAIKANAL SOLAR PROMINENCES DURING I912. — 



Bulletins Nos. 29 and 30 of the Kodaikanal Observa- 

 tory contain a summary of prominence observations 

 made at that observatory during the past year. Pre- 

 viously it was customary to publish detailed lists of 

 prominences, such as those which appeared in the 

 series of bulletins ending with No. 28, but these will 

 now be discontinued and replaced bv a re'sumi of the 

 observations issued half-yearly. This re'sume' will in- 

 clude full descriptions of any remarkable phenomena 

 observed or photographed, and, in addition to the 

 summary of the observations at the sun's limb, there 

 will be given the results of a study of the prominences 

 projected on the disc as hydrogen absorption markings. 

 The present two bulletins are written on these lines, 

 and they contain the summarised material for 1912. 



NO. 2277, VOL. 91] 



THE ALLOT ROPY OF IRON. 

 TWO papers read before the recent meeting of 



1 the Iron and Steel Institute, one by Dr. Car- 

 penter on the critical ranges of pure iron, and the 

 other by Dr. Rosenhain and Mr. Humfrey on the 

 tenacity, deformation, and fracture of soft steel at 

 high temperatures, were responsible for a renewal of 

 the discussion upon the allotropic modifications of 

 iron. The present discussion may be regarded as a 

 further contribution to an old controversy, and in 

 order to appreciate its true significance it is necessary 

 to review, somewhat in the manner of a serial story, 

 the incidents of the preceding chapters. 



In 1890 Osmond showed that when a piece of steel 

 was allowed to cool from a bright red heat the rate 

 of cooling was not uniform, but that at three points 

 there was an evolution of heat in the steel itself which 

 had the effect of retarding the fall in temperature 

 of the mass. These three arrests Osmond designated 

 as Ai, A2, and A3, Ai representing the change taking 

 place at the lowest temperature. In order to distin- 

 guish between the evolutions of heat during cooling 

 and the corresponding absorptions of heat during 

 heating, the letters r (refroidissement) and c (chanf- 

 fage) were added, and this nomenclature has been 

 retained, the irregularities in the cooling curve being 

 described as An, Ar2, and Ar3, and those in the 

 heating curve Aci, Ac2, and AC3. 



It was clearly shown by Osmond that the Ai change 

 was dependent upon the carbon in the steel, whereas 

 the points A2 and A3 were independent of the carbon 

 and equally prominent in the purest steel obtainable. 

 Osmond therefore argued that the thermal changes at 

 A2 and A3 must be due to molecular rearrangement 

 or allotropy in the iron. Iron above the A3 point he 

 described as y iron, that between the A3 and A2 points 

 iron, and below the A2 point a iron. 



Roberts Austen repeated and confirmed Osmond's 

 experimental work, and accepted his theory of allo- 

 tropy as being the most probable explanation of the 

 facts. Prof. Arnold, on the other hand, rejected the 

 allotropic theory on the ground that "steel research 

 was, in his opinion, a field of too national an import- 

 ance to be used lightly as a cantering ground for the 

 hobbies of periodicity and allotropy." After repeating 

 and confirming the work of Osmond and Roberts 

 Austen, Prof. Arnold suggested that the A3 point 

 was due to the influence of hydrogen, and the A2 

 point to a change from a plastic to a crystalline con- 

 dition. He contended that these changes had little 

 connection with the phenomena underlying the 

 hardening of steel, but that these were due solely to 

 the carbon, and at a later date he developed a sub- 

 carbide theory to explain the changes brought about 

 by hardening, &c. Further investigations, however, 

 bv independent metallurgists, tended to confirm 

 Osmond's original views, and within the last few- 

 years little has been heard of the controversy between 

 the " carbonists " and the " allotropists." 



The two papers which have been responsible for 

 the reopening of the discussion may be briefly sum- 

 marised as follows : — Prof. Carpenter, following a 

 hvnothesis of Benedicks, endeavours to prove that the 

 change at Ar2 is not an independent change, but 

 merely the tail end, or limit of supercooling due to 

 impurities, of Ar3. It may be mentioned that this 

 was Osmond's original explanation, which he aban- 

 doned when it was proved that the appearance of 

 magnetism coincided exactly with the point Ar2. 

 Prof. Carpenter argues that if Benedicks's theory is 

 correct pure iron should show the Ar2 change but 

 not the Ac2 change, and he gives a number of heating 

 and cooling curves of the purest iron obtainable in 



