Feb. 7, 1889] 



NATURE 



353 



ASTRONOMICAL PHENOMENA FOR THE 



WEEK 1889 FEBRUARY 10-16. 



/ "PrOR the reckoning of time the civil day, commencing at 



^ -^ Greenwich mean midnight, counting the hours on to 24, 



is here employed.) 



At Greenwich on February 10 

 Sun rises, yh. 24m. ; souths, I2h. 14m. 28*9s. ; sets, l^Y^. 4m. : 

 right asc. on meridian, 2ih. 37'Sta. ; decl. 14" ll' S. 

 Sidereal Time at Sunset, 2h. 28m. 

 Moon (Full on February 15, 22h.) rises, I2h. 7m. ; souths, 

 2oh. 12m.; sets, 4h. 23m.*: right asc. on meridian, 

 5h. 36-5m. ; decl. 21° i' N. 



Right asc. and declination 

 Planet. Rises. Souths. Sets. on meridian. 



h. m. h. m. h. m. h. m. . / 

 Mercury.. 7 23 ... 12 45 ... 18 7 ... 22 8-o ... 8 8 S. 

 \enus ... 8 41 ... 15 6 ... 21 31 ... o 29-9 ... 4 14 N. 

 Mars ... 8 28 ... 14 19 ... 20 10 ... 23 42-0 ... 2 39 S. 

 Jupiter... 4 46 ... 8 41 ... 12 36 ... 18 3-5 ... 23 6 S. 

 Saturn ... 16 18 ... 23 52 ... 7 26*... 9 lyi ... 17 i N. 

 Uranus... 22 37*... 40... 9 23 ... 13 2f9 ... 7 56 S. 

 Neptune.. 10 44 .. 18 27 ... 2 10*... 3 50-8 ... 18 25 N. 



* Indicates that the rising is that of the preceding evening and the setting 

 that of the following morning. 



Keb. 



IS 



Star. 



Mercury in inferior conjunction with the Sun. 

 Saturn in conjunction with and l° 5' south 

 of the Moon. 



Variable Stars. 

 R.A. Decl. 



h. m. , . h. m. 



U Cephei o 52*5 ... 81 17 N. ... Feb. 12, 19 30 m 



Algol 3 i-o ... 40 32 N. ... ,, II, o 59 w 



,, 16, 18 37 m 



A. Tauri 3 546 ... 12 il N , 13, 19 39 m 



CGeminorum ... 6 575 ... 20 44 N , 12, 6 o Af 



R Canis Majoris... 7 l/i'S ... 16 11 N. ... ,, 14, 20 7 m 



and at intervals of 27 16 



R Virginis 12 32-9 ... 7 36 N. ... Feb. 11, M 



U Coronae 15 137 ... 32 3 N. ... ,, 14, 20 34 m 



Y Cygni 20 47*6 ... 34 14 N 11, 5 40 »» 



and at intervals of 36 o 



» Cephei 22 2^-0 ... 57 51 N. ... Feb. 12, o o m 



R Lacertje 22 38-3 ... 41 47 N. ... ,, 15, Af 



M signifies maximum ; m minimum. 



Meteor-Showers. 

 R.A. Decl. 



From Camelopardalis 



, , Monoceros . . . 

 Near 5 Ophiuchi ... 



no .. 

 120 .. 

 263 .. 



62 N. 



ss. 



2N. 



Slow. 

 Slow. 

 Very swift. 



GROWTH OF OUR KNOWLEDGE OF THE 

 NEBULA. 



/^UR present knowledge of those celestial bodies which we 

 ^^ term nebulae may be said to date from a paper by Sir 

 William Herschel on nebulous stars, published in 1791 (Phil. 

 Trans., vol. Ixxxi. p. 71). It is perfectly true that we have not 

 here the first recorded observations of nebulce : several observers 

 before Sir William Herschel, and Sir William Herschel himself, 

 had previously referred to them. All observers previous to Sir 

 William Herschel, among whom we may include Kepler, Tycho 

 Brahe, Hailey, and others, were of opinion that the nebulae were 

 composed of something differing entirely in its essence from 

 stars. There was no question whatever of their being simply 

 clusters of stars considerably removed. Tycho Brahe, in the 

 record of his observations of the new star observed by him in 

 Cassiopeia, suggested that it was in some way generated from 

 an ethereal substance, and to him the Milky Way was composed 

 of the same material. This ethereal substance was liable to 

 dissipation by light and heat, and in this way he accounted for 

 the ultimate disappearance of the star. Kepler shared this 

 opinion, and it may be stated that it was generally accepted at 

 the time that Sir William Herschel began his observations of 

 nebulae about the year 1780. His first important paper, how- 

 ever, did not deal with these objects : it had reference to the 



motion of the sun in space (Phil. Trans., vol. Ixxiii., published 

 in 1783). In this memoir he points out the universal sway of 

 gravitation in the celestial spaces ; and the infinite possibilities 

 opened out by such an all-prevailing and pervading cause seem, 

 although he does not state it in terms, to have led him to the 

 conclusion that such ideas as Brahe's and Kepler's were invalid. 

 His first real survey of the nebulae appears in his paper of 1784 

 (Phil. Trans., vol. Ixxiii.) He began by observing those bodies 

 which had already been recorded in the Connaissattce des 

 Temps for 1783, and then those further afield ; and it is not a 

 little remarkable that in this first paper he describes almost every 

 distinct form of nebulae which has been observed from that day 

 to the years about 1846, when Lord Rosse brought a still 

 more powerful instrument than Herschel's largest to bear upon 

 these objects. He noticed that in certain parts of the heavens 

 there was a marked absence of stars, and that this was so 

 invariably followed by the appearance of 'nebulae on the confines 

 of the empty region that he records in his memoir that after 

 passing over one of them he was in the habit of giving the 

 word to his assistant to " prepare for nebul<e." This strengthened 

 his view as to the power of gravitation, and as to nebulae being 

 masses of stars produced by it. 



In another paper published in the next year (Phil. Trans., vol. 

 Ixxv.) he shows evidently that to him the nebulae of all orders 

 which he had discovered were simple agglomerations of stars, 

 and he refers to the action of gravity in bringing about such 

 condensations. In the next year (Phil. Trans., vol. Ixxvi. ) he 

 published the first catalogue of a thousand nebulae, and gives his 

 first classification, one based upon brightness (p. 466). In 1789, 

 that is three years later (Phil. Trans., vol. Ixxix.), he published 

 his second catalogue, and it is clear from the text that he still 

 considered nebulae to be all distinct star clusters. It required 

 another interval of three years before the possibility of their 

 nature being in any way distinct was brought fairly before his 

 mind. In 1791 (Phil. Trans., vol. Ixxxi.) he published his 

 remarkable paper on "Nebulous Stars properly so-called." In 

 this paper it will be seen how convincing was the line of argu- 

 ment which Herschel followed to bring him ultimately to the 

 conclusion that in the bodies which he observed there was either 

 a central body which is not a star, or a star involved in a 

 shining fluid of a nature totally unknown to us (p. 83). 



This conclusion seems to have made a profound impression 

 upon Herschel's mind, and we had to wait for ten years before 

 he returned to the subject. He did so in 1801 (Phil. Trans., 

 vol. ci.), in a paper detailing " Astronomical Observations relat- 

 ing to the Construction of the Heavens, arranged for the purpose 

 of a critical examination, the result of which appears to throw 

 some new light upon the organization of the celestial bodies." 

 In this paper he classifies all the different k inds of nebulae which 

 were then known to him, and specimens of which, as has been 

 before stated, he really seems to have glimpsed in his paper of 

 1784. He points out that, in the classification which he proceeds 

 to give, the bodies under consideration are treated in such a 

 manner that each shall assist us to understand the na;ure and con- 

 struction of the others ; and he endeavours to attain this end by 

 assorting them into as many classes as are required to produce 

 the most gradual affinity between the individuals contained in 

 any one class and those contained in that which precedes and 

 that which follows it (p. 271). He remarks: "This consider- 

 ation will be a sufficient apology for the great number of assort- 

 ments into which I have thrown the bodies under consideration." 

 His classification may be stated as follows : — 

 I. Extensive diffused nibulosity. — Under this title he in- 

 cludes faint nebulosities stretching and branching over various 

 portions of the sky, which he was the first to discover by means 

 of the enormously increased optical power which he brought to 

 bear. He states that "they can only be seen when the air is 

 perfectly clear, and when the observer has been in the dark long 

 enough for the eye to recover from having been in the light 

 (p. 274). He gives fifty-two of these diffused nebulosities, 

 which he had ob.-erved in the nineteen years from 1783 to 1802. 

 He remarks that "extensive diffused nebulosity is very great 

 indeed; for the amount of it, as given in the tables, is 151 7 

 square degrees ; but this, it must be remembered, gives us by 

 no means the real limits of it;" and he finally adds, "it will 

 be evident that the abundance of nebulous matter diffused 

 through such an expansion of the heavens must exceed all 

 imagination." 



2. Nebulosities joined to nebuUe. — He refers to fourteen 



