Nov. 24, 1887] 



NATURE 



83 



It will be observed, too, that the information in some cases is 

 fuller in the blue part of the spectrum. Here again a reference to 

 what the maps are really intended to show is necessary. The maps 

 do not show the complete spectrum observed, but only the bright 

 lines recorded in it. The actual observations liave really consisted 

 in picking out these bright lines from the background of con- 

 tinuous spectrum, whether in stars, nebuLie, or co.nets ; and, as 

 the continuous spectrum will be generally brightest in the yellow 

 and green, so in this part of the spectrum we must expect, first 

 of all, to get the least information, and then, when the infor- 

 mation is obtained, to get the greatest uncertainty, on account 

 of the difficalty brought about by the greater luminosity of the 

 background on which the line appears. 



The discussion by Ma^selberg and others of the various ob- 

 servations of comets which have been made from time to time 

 indicates that under certain circumstances, where men of the 

 highest skill and with the greatest care have determined the 

 wave-lengths of the carbon bands, discrepancies exist too great 

 to admit of their being attributed to errors inherent in this branch 

 of observalioi. 



If for a moment we consider alone the two bright fluting? 

 visible in the spectrum of carbon, one with its bright edge just 

 more refrangible than b^^ — this is the high-temperature spectrum 

 — and the other — tlie low-temperature spectrum — with a fluting 

 just less refrangible than l\, it is at once suggested that sudden 

 changes in comets may very likely be accompanied by a transi- 

 tion from one condition of carbon vapour to the other, so that 

 on this account apparent discrepancies in the measurements of the 

 same comet at different times may represent real facts. Then 

 again we have the motion of the swarm along its orbit, which 

 in some cases we know is comparable to the velocity of light, so 

 that variations of wave-length are produced as indicated in 

 comet 1882. We also have the possibility that j the velocity of 

 the vapours in the jets, and that due to the electric repulsion — 

 which, according to ZoUner's view, is the origin of comets' 

 tails — may also produce changes of refrangibility. 



Although as a rule the bright fluting seen in comets appears 

 to be that due to high temperature, this is apparently not always 

 the case. In the experiments on the glow of magnesium wire, 

 the flutings of carbon have always been seen, and when the 

 vacuum is approached the flutings have been those of the low- 

 temperature spectrum. When the glow of the metal is seen 

 under certaii conditions, mixed with carbon vapour, b^ and b<i^ 

 are seen as bright dots or short lines inside the carbon fluting, 

 exactly as they were observed, probably, by Huggins in Brorsen's 

 comet (Proc.R. S., vol. xvi. p. 386). 



Authorities used in the Maps. 



The map showing the bright lines in Stars is based upon the 

 following authorities : — 



3rd Cygnus, B.D. -f- 36° No. 3956, R.A. 2oh. lom. 6j., 

 Dec), -f- 36° 18'. 

 Vogel. — Ptiblicationen des Astrophysikalischen Observa- 

 toriums zu Potsdam, vol. iv. No. 14, p. 19. 



2nd Cygnus, B.D. 4- 35', No. 4013, R.A. 2oh. 7m. 26s., 



Decl. + 35' 50' -8. 

 Vogel. — Publicalionen des Astrophysikalischen Observa- 



toriums zu Potsdam, vol. iv. No. 14, p. 19. 

 Wolf and Rayet. — Comptes renins, vol. Ixv. (1867), 



p. 292. The wave lengths were obtained from a 



curve based on the measurements given. 



Argelander-Oeltzen 17681, R.A. i8h. im. 21s., Decl. - 21" 

 1 6' -2. 

 Vogel. — Publicationen des Astrophysikalischen Observa- 



toriums zu Potsdam, vol. iv. No. 14, p. 15. 

 Pickerin.j. — Astronomische Ncuhrichten, No. 2376. 

 Pickering. — Observatory, vol. iv. p. 82. 



7 Argus, R.A. 8h. 5m. 56s., Decl. - 46° 59'*5. 

 Copeland. — Copernicus, vol. iii. p. 205. 

 EUery. — Obiervatory, vol. ii. p. 418. 



Stone 9l68(starin Scorpio), R.A. i6h. 46m. 15s., Decl. - 41° 

 37'-6. 

 Copeland. — Copernicus, vol. iii. p. 205. 



1st Argus, R.A. 8h. 51m. is., Dec'. - 47° 8'. 



Copeland. — Copernicus, vol. iii. p. 206. 

 2nd Argus, R.A. loh. 36m. 54s., Decl. - 58' 8'. 



Copeland. — Copernicus, vol. iii. p. 236. 

 Gould 15305 (Argo), R.A. iih. 5m. i;s., Decl. - 60° 2l'. 



Copeland. — Copernicus, vol. iii. p. 2o5. 



Star in Centauri, R.A. I3h. ion. 373., Decl. - 57" 31'. 

 Copeland. — Copernicus, vol. iii. p. 206. 



Star in Cygnus, B.D. + 37° No. 3821, R.A. 2oh. 7m. 48s., 

 Decl. -f 38° o'-i. 

 Copeland. — Monthly Notices of the Royal Astronomical 

 Society, London, vol. xlv. p. 90. 



Lalande 13412, R.A. 6h. 49m. 15s., Decl. - 23" 46'*3. 



Vogel. — Publicationen des Astrophysikalischen Observa- 



toriums zu Potsdam, vol. iv. No. 14, p. 17. 

 Pickering. — Astronomische Nachi'ichten, No. 2376, 



1st Cygnus, B.D. 4- 35° No. 4001, R.A. 2oh. 503. 48s., Decl. 

 + 35° 49'7- 

 Vogel. — Publicationen des Astrophysikalischen Ohserva- 

 toriums zu Potsdam, vol. iv. No. 14, p. 17. 



y Cassiopeise, R.A. oh. 50m. 45., Decl. -I- 60° 7'"2. 



Vogel. — Publicationen des Astrophysikalischen Observa- 



toritims zu Potsdam, vol. iv. No. 14, p. 15. 

 Vogel. — Beobachtungen zu Bothkamp, Heft ii. p. 29. 

 Gothard. — Astronomische Nachrichten, No. 2581. 

 Konkoly. —Quoted by Gothard in Astronomische Nach- 

 richten, No. 2581. 

 Observatory, vol. vi. p. 332. 



/3 Lyrae, R.A. i8h. 45m. 55s., Decl. -f 33' i3'-9. 



Vogel. — Publicatiomn des Astrophysikalischen Observa- 



toriums zu Potsdam, vol. iv. No. 14, p. I5- 

 Vogel. — Beobachungen zu Bothkamp, Heft i. p. 33. 

 Gothard. — Astronomische Nachrichten, No. 2581. 



The map showing the bright lin 2s in Ncbulce is based upon the 

 following authorities : — 



Nebula in Orion. 



Hujgins — Proceedings R.S. vol. xiv. p. 39. 



Planetary Nebula, R.A. 2lh. 22m., D.-cl. -f 47° 22'. 

 Copeland. — Copernicus, vol. i. p. 2. 



Planetary Nebula. 



Vogel. — Mmitsberichte der Akademi: der Wissenschaften 

 zu Berlin, April 1878, p. 303. 



No. 4572, 2075h., 16 H. iv. R.A. 2oh. i6m. 7-93., N.P.D. 

 70° 20' 1 9" -3. 

 Huggins.— Philosophical Transactions, vol. clvi. p. 38$. 



Comet 1866. 



Huggins. — Proceedings R.S. vol. xv. p. 5. 



Nova Cygni. 



Lord Lindsay and Dr. Copeland. — C^/^r«/(rM.r, vol. ii. 

 p. 109. 



The map showing the coincidences of flutings of carbon, 

 manganese, and zinc, with bright lines and flutings in stars and 

 comets, and i 1 a meteorite glow, is based upon the following 

 authorities : — 



Hydrocarbon "\ 



Low-temperature carbon ... |- Work at Kensington. 

 High-temperature carbon ... J 



Comet b 1881. 



Copeland.— Cc/^;-«V«.f, vol. ii. p. 225. 



Manganese flame. ^^ 



Lecoq de Boisbaudran.— " Spectres Lumineux. 

 Work at Kensington. 



Nova O.ionis. 



Copeland.— il/*^^//^// Notices of the Royal Astronomical 

 Society, vol. xlvi. p. 109. 



