212 



NATURE 



[November 15, 1917 



OUR ASTRONOMICAL COLUMN. 



November Meteors. — The moon being absent this 

 year at the epoch of the Leonids, a favourable oppor- 

 tunity will occur, should the atmosphere be clear, for 

 re-observihg the shower. The parent comet (Tempel 

 1866 I.) is, however, now near aphelion, and there is 

 little prospect of witnessing an abundant display. But 

 some of the swift, streaking meteors directed from the 

 "Sickle of Leo" are visible every year, and may well 

 repay observation on the morning of November i6. 



There is another shower, possibly more irregular and 

 uncertain in its returns, connected with Biela's comet. 

 These meteors, radiating from near y Andromedae, 

 travel very slowly, as they are moving in the same 

 direction as the earth and have to overtake us. They 

 are due on the nights from November 19 to November 

 22, and may be observed at any hour. These Andro- 

 medids were seen in 1872, 1885, 1892, 1899, and 1904, 

 but have not reappeared in plentiful numbers since the 

 last-named year. The parent comet has not been seen 

 since 1852, though it must have made nine returns 

 to perihelion, the periodic time being about 6-6 years. 



Encke's Comet. — It is curious that although this 

 comet was photographed a year ago, when close to 

 its aphelion, yet repeated search in the present autumn 

 has failed to reveal it. The object observed for it in 

 mid-September by Wolf proves not to be a comet, but 

 a minor planet. It has been designated CP, and the 

 following orbit published : — 



Epoch 1917 October 3-5 G.M.T. 

 M 29° 5"6' ^ 1 1° 30*4' 



« 39° 44"2') w 1057-9" 



Q 285° 437' ^19170 log a 0-35038 



z 4° 437'J Period 3 354 y. 



It will be recalled that in January, 1908, Prof. Wolf 

 announced an object as Encke's comet that proved to 

 be an independent comet. The very large value 3-84 

 was found for its perihelion distance, but the observa- 

 tions were too few to give trustworthy elements. 



Effective Wave-lengths of Clusters and Spiral 

 Nebula. — A new series of determinations of the effec- 

 tive wave-lengths of certain spiral nebulae and globular 

 clusters has been made at Upsala by K. Lundmark 

 and B. Lindblad (Astronomische Nachrichten, 4907). 

 The method employed was that in which a coarse grat- 

 ing, with spacing in this case of 1-3422 mm., is fixed in 

 front of the object-glass of a photographic telescope. 

 Some of the results are as follows : — 



Object Mag. Effective 



■^ " wave-length 



Cluster M5 ... 67 ... 4191 



„ M3 ... 6-6 ... 4251 ... F5 



Spiral M94 ... 77 ... 4267 ... G 

 „ M51 ... 8-4 ... 4307 ... G5 

 M64 ... 8-6 ... 4338 ... K 

 A Faint Star as near as a Centauri. — In Circular 

 No. 30 of the Johannesburg Observatory attention was 

 directed by Mr. Innes to a faint star in Centaurus 

 which had been found to have the large proper motion 

 of about 5" per annum. Mr. J. Voute, of the Cape 

 Observatory, now announces (Monthly Notices, 

 R.A.S.,- vol. Ixxvii., p. 650) that the parallax and 

 proper motion of this star are nearly identical with 

 those of a Centauri, which is still the nearest star 

 known. Mr. VoOte finds the parallax to be 0755", and 

 the proper motion 376" in the direction 2827°, while 

 the corresponding figures for o Centauri are 0759", and 

 3-68" in the direction 281-4°. It will be seen that the 

 agreement is extraordinarily close, although the dis- 

 tance between the two stars is 2° 12'. The question is 

 raised as to whether the stars are physically con- 

 nected, or are members of the same drift. 



NO. 2507, VOL. 100] 



Spectrun 

 inferred 



F 



The visual and photographic magnitudes of the faint 

 star are respectively ii-o and 13-5, so that the spec- 

 trum is probably of type M. The magnitude reduced 

 to a distance of 10 parsecs is 15-4, or 17-9 photographic- 

 ally, and the star would thus appear to be the 

 faintest at present known. 



The position of the star for 1916-11 is R.A. I4h. 

 23m. 54-28s., declination —62° 19' lo-i". 



PYROMETERS AND PYROMETRY. 

 T^HE meeting of the Faraday Society on November 7, 

 -*■ at the Royal Society of Arts, Sir Richard Glaze- 

 brook occupying the chair, was devoted to a general 

 discussion on "Pyrometers and Pyrometry." From 

 the character of the papers read and the remarks of the 

 various speakers, it may be inferred that present-day 

 activities in this direction are mainly devoted to apply- 

 ing existing instruments to industrial uses, rather than 

 to the development of new methods of measuring high 

 temperatures. The extent to which pyrometers are 

 now employed may be gauged from the fact that one 

 armament firm alone has six hundred instruments in 

 daily use, and in all branches of industry where accu- 

 rate temperature control is necessary pyrometers now 

 form an indispensable part of the equipment. 



In this country the standardisation is undertaken by 

 the National Physical Laboratory. At the outbreak of 

 the war negotiations were in progress with a view to 

 the production of an international scale of temperatures, 

 in the absence of which a provisional scale has been 

 adopted for present purposes. Dr. Ezer. Griffiths and 

 Mr. F. H. Schofield, on behalf of the N.P.L., gave an 

 account of this scale, and also of the methods adopted 

 in standardising pyrometers of various types. A strik- 

 ing confirmation of the value of central standardisation 

 was furnished later in a paper read by Prof. 

 J. O. Arnold, who, in experiments on the quenching 

 of high-speed steels, used four different types of pyro- 

 meters to control the temperature of a barium chloride 

 bath. The agreement of the instruments near to 

 1300° C. was remarkably good, and proved that any 

 of the four could have been relied upon to regulate the 

 temperature independently. 



The types of pyrometers now used industrially are 

 chiefiy the thermo-electric, for. temperatures up to 

 1200° C, and total radiation and optical pyrometers 

 for higher temperatures. The chief drawback to the 

 thermo-electric instrument is the error caused by fluc- 

 tuations in the temperature of the cold junction, to 

 obviate which various devices have been introduced 

 from time to time. Mr. R. S. Whipple suggested that 

 this trouble might be overcome by burying the cold 

 junction in the ffround to such a depth that any tem- 

 perature variations would be negligible. From experi- 

 ments conducted at Cambridge, and extending over 

 three years, it was found that at a depth of 10 ft. 

 the variation in temperature was only i-6°. It was 

 pointed out, however, that in the vicinity of a group 

 of steel furnaces it would be necessary to locate the 

 cold junction at a much greater depth than 10 ft. to 

 secure anything approaching constancy, and that in 

 consequence the method would have a limited applica- 

 tion in practice. With regard to optical pyrometers, 

 it was rather disquieting to learn that the mono- 

 chromatic glass used in some of these instruments 

 could not yet be produced in England. Pre-war sup- 

 plies were of German origin, and at present this indis- 

 pensable material is obtamed from the United States. 

 It is to be hoped that one of our own glass firms will 

 take this matter in hand, particularly in view of the 

 rapid extension of the use of optical pyrometers. 



Several of' the papers read bore on the temperature 

 of molten steel, and the discussion made it clear that 

 steel-makers now attach great importance to the tem- 



