404 



NATURE 



[August 21, 1890 



OUR ASTRONOMICAL COLUMN. 



Objects for thk Spectroscope. 



Sidereal Time at Greenwich at lo p.m. on August 21 = 

 2oh. cm. 4IS. 



Remarks, 



(i) This is the so-called "Dumb-bell Nebula." Dr. Huggins's 

 record of the spectrum is as follows : — " The light of this 

 nebula, after passing through the prisms, seemed concentrated 

 in a bright line. This line appeared nebulous at the edges. 

 No trace of the other lines was perceived, nor was a faint con- 

 tinuous spectrum detected. The light from different parts of 

 the nebula is identical in refrangibility, and varies only in 

 degree of intensity." The line referred to is, of course, the 

 chief nebula line, near \ 500, and it will be seen that in this 

 case it was not perfectly sharp and well-defined. It is important 

 that the observation should be repeated by as many impartial 

 observers as possible, as there is still a difference of opinion as 

 to whether the line is really sharply defined or not. Other 

 lines may also be looked for. Prof. Winlock simply observed 

 that the spectrum consisted of a single line, and no continuous 

 spectrum. 



(2, 3, 4) These are the three "bright-line stars " first observed 

 by Wolf and Rayet in 1867, and called by them ist, 2nd, and 

 3rd Cygnus, respectively. They were subsequently observed in 

 greater detail by Vogel, who found that many lines were 

 comnion. It has been shown that most of the lines can be 

 explained by a reference to the low-temperature spectra of 

 manganese, iron, and sodium, in addition to the radiation of 

 hydrogen and carbon. The most striking feature of the spectra 

 is undoubtedly the bright band in the blue, which, standing 

 out beyond the continuous spectrum, gives rise to an apparent 

 absorption band on the less refrangible side. My own observa- 

 tions, and those of Mr. Lockyer, have shown that this band is 

 coincident with the blue band seen in the spectrum of the spirit- 

 lamp flame, and is therefore probably due to carbon. This con- 

 clusion is supported by the presence of another carbon fluting, 

 near A 5 1 7, which, however, is not so obviously seen because of 

 the brighter continuous spectrum in that region. These are the 

 brightest bands seen in the spectra of comets at mean distances 

 from the sun, and the similarity leads to the conclusion that the 

 structure of comets and bright-line stars is identical (see Nature, 

 August 7, p. 344). Bright-line stars are therefore probably 

 swarms of meteorites. It is desirable that the coincidence of the 

 carbon bands with those of the " stars " should be confirmed by 

 other observers. 



(5) The spectrum of this star is a well-marked one of Group 

 II., the bands 2-9 being wide and dark. It is probably one of 

 mean condensation, and the bright carbon flutings should there- 

 fore be well seen. It will be interesting also to know what dark 

 iines, if any, are present at this stage. 



(6) A star of the solar type (Vogel). Is the temperature 

 increasing (Group III.) or decreasing (Group V.)? 



(7) A star of Group IV. Observations of the comparative 

 intensities of the hydrogen and other lines are required, in order 

 that the temperature relatively to other stars of the group may 

 be determined. 



(8) This is a relatively bright star of Group VI., showing 

 the secondary bands 2, 3, 4, 5, and 8, in addition to the usual 

 carbon bands, which are very wide and dark. As in other stars 

 of the group, further details, especially the presence or absence 

 of solar lines, should be looked for. 



(9) This variable of Group VI. will reach a maximum about 

 August 25, the period being about 485 days. The magnitude 

 at maximum is 7-4-8 -5, and that at minimum about 11-5. I 

 may repeat that we as yet know nothing of the spectroscopic 



NO. 1086, VOL. 42] 



changes which accompany the increase of light in a star of this 

 kind, and continuous observations will therefore be of the utmost 

 value. It has been suggested by Mr. Lockyer that the chief 

 variation may be the relative paling of the principal bands at 

 maximum. Colour changes should also be noted. 



A. Fowler. 



Moscow Observatory.— Prof. Th. Bredichin has issued the 

 second volume of the second series of Annales de P Observatoire 

 de Moscou, and it contains some interesting papers. In one 

 "On the Origin of Periodic Comets," Prof. Bredichin brings 

 forward many important facts. He first points out the similarity 

 of the elements of some comets, and adduces evidence to show 

 that they probably once formed part of a single comet which has 

 become disintegrated by explosions and planetary perturbations ; 

 the multiple comets of Biela, Liais (i860), and 1882 II. being 

 quoted as examples of such a development. After deducing the 

 expressions for eruptions which do not take place in the plane of 

 the orbit of the generating comet, and applying them to some 

 examples, the elements of twenty-nine comets having a period 

 less than 100 years is given, and some considerations relative to 

 their perihelion distances, small inclinations, and direct move- 

 ment are urged, as opposed to the hypothesis of the immediate 

 transformation of parabolic to elliptic orbits. Two tables of 

 290 non-periodic comets arranged in the order of their perihelion 

 distance {q), and 44 comets which have developed comae, will be 

 useful, irrespective of the fact that they demonstrate that when 

 the value of q is sensibly greater than I the comet has little 

 ability to develop eruptive phenomena and to produce new 

 comets. A division of periodic comets into four groups is made, 

 the periodic time of the respective groups being 73'8, 33'i, 

 14' I, and 6*o years, and it is shown that the values of the 

 eruptive action increases as the period decreases. The influence 

 of Jupiter and Saturn on cometary orbits is, of course, con- 

 sidered, and some relations are pointed out between the times 

 of revolution of the above-mentioned groups and those of these 

 two planets. In another long paper " On the Origin of Shoot- 

 ing Stars," Prof. Bredichin attempts to prove that all meteors are 

 ejections from comets. A paper by M. P. Sternberg gives the 

 results of some determiuations of the length of the seconds 

 pendulum made by Prof. Bredichin and himself in 1888-89 in 

 various parts of Russia and Europe ; and another paper, by M. 

 Ceraski, "On Luminous Clouds," contains some interesting facts. 

 On June 26, 1885, from observations made at two stations, 

 separated by 10 kilometres, the vertical height of a luminous 

 cloud was found to be nearly 75 kilometres. A map is also 

 given for putting down observations of the paths of Perseid 

 meteors, and this, with the eleven papers, renders the volume 

 for 1890 as good as its predecessors. 



Leander McCormick Observatory. — Vol. i., Part 4, of 

 the Publications of the Leander McCormick Observatory of the 

 University of Virginia contains some double-star observations 

 made in 1885-86. The working list from which the double 

 stars were selected contained all known pairs between —30° and 

 0° having distances less than 4", and several very close and diffi- 

 cult pairs north of the equator. The observers were Messrs. 

 F. P. Leavenworth and Frank Muller, and the measures appear 

 to have been made with much care. 



Coggia's and Denning's Comets (b and c 1890).— The 

 following ephemerides are given by Dr. Berberich in Astrono- 

 mische Nachrichten, No. 2984 : — 



Ephemerides for Berlin Midnight. 



