♦ KNOWLEDGE ♦ 



[July 1, 1889. 



PHOTOGRAPHS OF NEBULA. 



By A. C. Ea^yakd. 

 THE SPIRAL NEBULA IX URSA MAJOR. 

 81 Messier (G.C. 1949). 

 As shown on Mi\ Isaac Roberts' photograph, this is a 

 fine example of a spii-al nebula, though up to the date of his 

 photograph its spiral character had not been recognised. Dr. 

 Copeland, using the Earl of Eosse's 3-foot reflector, describes 

 it as very like the great nebula in Andromeda, though at the 

 time of the observation (1871) the spiral character of the 

 Andromeda nebula had not been recognised. With the 6-foot 

 reflector in 1874, he found that the nebulosity extended about 

 eight minutes of arc from the nucleus towards the north, 

 and that the fainter portion was elongated in the north 

 preceding and south following directions. He describes it 

 as " extremely bright, very suddenly very much brighter in 

 the middle to a nucleus." From Mr. Roberts' photograph it 

 is evident that the plane of the spiral is inclined to us, so 

 that the longer axis of the ellipse into which it projects is 

 inclined in a north preceding and south following direction, 

 as described by Dr. Copeland. The longer diameter of the 

 ellipse is more than sixteen minutes, so that Dr. Copeland 

 must have seen the parts of the nebula which Mr. Roberts' 

 photograph shows to break up into spiral streams. Upon 

 the stream lines of these faint spii-al arms are a number of 

 nuclei or possibly small stars, which reminds one of the 

 arrangement of stars on the stream lines of the Andromeda 

 and Canes Venatici nebulae. There are no outlying smaller 

 nebulae, in the immediate neighbourhood of this spii-al 

 nebula as in the case of both the above-mentioned larger 

 spirals. But the spiral structure of this nebula seems to 

 be more regular. But about 42 minutes to the north 

 of it lies a most remarkable elongated nebula known as 

 82 Messier (G. C. 1950). Towards its centre are two 

 nuclei, each of which are double. The ray is divided in a 

 transverse dii-ection by two very marked dark channels. 

 Ingall describes it in the English Mechanic for December 18, 

 1885, as having a twisted appearance like a ''distaff of 

 flax." The longer axis of this remarkable nebulous ray is 

 inclined in a north preceding and south following direc- 

 tion. Huggins has found the spectra of both these nebulae 

 to be continuous, but deficient towards the red end. 



THE SPIRAL NEBULA IN CANES VENATICL 

 51 Messier (G.C. 3572). 

 This interesting nebula has been drawn by, amongst others, 

 Sir John Herschel (see " Phil. Trans." for 1833), Lord Eosse 

 (" Phil. Trans." 1850), Lassell (" Memoirs of the R. A.S.," vol. 

 XXXV.), andby Vogel (see " Potsdam Observations," vol. iv.). 

 Sir John Herschel's drawing only shows a partly split ring 

 round a nebulous centre, with a small detached nebula to the 

 north. Smaller instruments only show two unequal nebuke 

 nearly in contact. Sir John Herschel had an idea that there 

 was an analogj' between this nebula and the split ring of the 

 Milky Way ; but we now know that the nebula has a most 

 complicated form. In addition to the spiral streams about 

 the chief nucleus, there is a curved nebulous stream which 

 joins the secondary nucleus towards the north, and an 

 appearance as of a smaller spiral system about one of 

 the stellar points on the preceding branch of the great 

 spiral. The aggregation of stars or nebulous masses along 

 the stream lines of nebulous matter is very marked. The 

 smaller nebulous mass towards the north is cut off sharply 

 on the following side. The nebulous stream which joins it 

 to the great spii-al comes up to its northern side ; and on 

 Mr. Roberts' negative there is an appearance of spiral 

 structure even about this smaller nebula. Mr. Common 

 obtained an excellent photograph of this nebula with his 



3-foot reflector at Ealing about four years ago. The nebu- 

 lous streams of this complicated structure are so marked that 

 they were recognised by observers before the photographic 

 era. The Earl of Eosse's drawing is perhaps the best of any 

 made with his great telescope. It shows nebulous matter 

 filling up the spaces between the great streams more than 

 any other drawing. Mr. I.assell's drawing, and the one 

 made by Dr. Vogel with the 27-inch refractor at Vienna, 

 are also very good. Dr. Huggins finds the spectrum 

 continuous. 



THE DUMB-BELL NEBULA IN VULPECULA. 

 27 Messier (G.C. 4532). 



The brighter parts of this nebula are very conspicuous, and 

 in a small telescope resemble a dumb-bell in form, hence its 

 popular name. It has been figured by a great many ob- 

 servers, amongst others Sii- John Herschel, in the " Phil. 

 Trans." for 1833; by the Earl of Eosse, in the "Phil. 

 Trans." for 1844, 1850, and 1861 ; by Secchi, in the 

 " Memorie dell' Osservatorio del Collegio Romano." 1852- 

 55, plate iv. ; by Smyth, in the " Speculum Hartwellianum," 

 p. 290 : by D' Arrest, in the " Instrumentum Magnum 

 .■Equatoreum ; " by Trouvelot, in vol. vii. of the " Annals of 

 the Harvard College Observatory ; " and by Vogel, in 

 vol. iv. of the " Publications of the Potsdam Observatory ; " 

 and by Ingall, in the Emjlisli Meclianic for December 

 1874. Mr. Lassell gives a map of the stars in and about 

 the nebula on a scale of 100 seconds to the inch in vol. xxxv. 

 of the " Memoirs" of the R. A.S. 



Mr. Roberts' photograph shows a brighter edge to the 

 northern lobe of the dumb-bell, which is not shown in the 

 drawings. The fainter nebulous matter, which forms the 

 background on which the dumb-bell is seen, projects beyond 

 the elliptic outline. It appears to be structureless, but the 

 brighter region of the nebula breaks up into curdling masses 

 of greater density. Several stars are seen projected on the 

 nebula, one nearly centrally. The drawing which appears 

 to me most nearly to represent the appearance seen on Mr. 

 Roberts' negative is that by Father Secchi. According to 

 Dr. Huggins, the spectrum of this nebula consists simply of 

 one bright line. 



STAR-BORN METEORS. 



By the late Rk hard A. Pboctor. 

 (Continued from 2^- 16.) 

 irCH was the position, on the one hand of 

 meteoric astronomy, and on the other of the 

 various theoretical conclusions which wer& 

 either demonstrably deducible from dis- 

 covered facts, or seemed more or less pro- 

 bable as viewed in their light. Putting all 

 theory aside, so much as this was certain, 

 /ind is certain, — among the meteoric streams encountered 

 by the earth each yeai-, some are undoubtedly travelling in 

 elliptical orbits around the sun ; and among these some are 

 as certainly following in the tracks of known comets. 

 Moreover, among all the paths thus determined, none are^ 

 of such extent that the velocities of the meteors where they 

 cross the earth's track exceed enormously the velocity of the 

 earth in her orbit. 



This being so, students of meteoric astronomy heard, 

 with some surprise, an announcement by ]Mr. Denning four 

 or five years ago, that he had discovered certain systems of 

 meteors which could not possibly be explained by anything 

 thus far demonstrated respecting these bodies. It was not 

 in such terms, indeed, that he announced his discovery, but 

 that was undoubtedly what it amounted to. He stated that 



