Feb. 14, 1878] 



NATURE 



313 



others. It is, besides, the brightest of them all. Extensive 

 investigations published on this subject cannot, however, be said 

 fully to elucidate the question why the other lines of nitrogen 

 do not appear in the spectrum, nor do physicists agree as to the 

 temperature and density which, under these circumstances, must 

 be supposed in the nebulae. It is, besides, precarious to draw 

 from phenomena observed in Geissler's tubes conclusions as to 

 circumstances prevailing in the vast nebul::e (Zollner, Berichte der 

 k. sachsischen Gesellschaft d. JVissensck, for 1870, p. 254). It 

 appears less important that nobody has been able to comply with 

 Angstrom's demand when he says (" Recherches sur le Spectre 

 solaire," p. 37) : — "This line is double. ... It appears, there- 

 fore, that we ought to be able to show this duplicity in the cor- 

 responding line of the nebular spectrum." To their separation 

 is required too narrow a slit for the feeble light of the nebulae. 

 All considered, nitrogen is at present very likely one of the 

 constituents of nebulce. 



The origin of Neb. (2) is not known. The idea at first occurred 

 to Huggins of one of the many barium-lines, but he soon gave 

 this idea up. One of the iron lines holds exactly its place ; it is 

 a dark line, but not one of the principal of the rich spectrum ; 

 of course this coincidence is accidental. This line is again met 

 with in the spectrum of many red and variable stars. The 

 measures of Vogel {Ber. d. k. sacks. Gcsellsch, d. Wissensch., 1871, 

 December 17) agree well enough with the gaseous line when the 

 great difficulties of the cases are taken into account. A^eb. (2) 

 does not occur in the spectra of comets. 



A^eb. (3) is identical with the line H;3 of hydrogen, whose 

 existence in gaseous nebulae was proved when Huggins discovered 

 Neb. {4), which is H7, that was so long sought for in vain. 

 Hydrogen is everywhere found as one of the constituents of the 

 heavenly bodies, but the comets contain no traces of it. The 

 hydrogen-lines appear even in the spectra of many fixed stars, at 

 least through Ho and Hy3, but sometimes H;3 and H7 are the 

 strongest (/8 Lyrae), and three hydrogen lines are distinctly seen 

 in the spectra of a Aquilse and a Lyrae. 



D' Arrest then gives in his paper a list of all the nel)ulsc 

 which have been spectroscopically examined by himself or others. 

 He speaks first of the gaseous nebulae, of which H. iv. 37 is 

 the most remarkable ; then he mentions those whose spectra are 

 continuous, and thus proved to be mere conglomerates of stars. 

 The latter are by far the most difficult to examine, the feeble light 

 being distributed over a large space, and generally minima 

 visibilia. An astronomer well versed in the use of the spectro- 

 scope is, however, often able to decide whether the spectrum is 

 continuous, even if it be not visible by glimpses. Already 

 the absence of the spectrum may occasionally hint about 

 the true nature of the body. He estimates the number of 

 nebulae known in the middle of 1872 to be about 6,000 ; of these 

 150 have been examined with the spectroscope. It is, therefore, 

 only the foitieth part, which is bright enough to be seen through 

 the system of prisms. Although it is hardly possible to draw 

 conclusions from so small a fraction of the whole, still d'Arrest 

 thinks it possible, on account of the critical revision he has 

 given the observations, to arrive by induction at a few results. 

 He finds that of a given number of nebulas about a fourth 

 give the discontinuous spectrum, while three-fourths give the 

 continuous. 



Gas nebulae are, with but few exceptions, known by their 

 green-blue light, their sharply-defined, round, or elliptic discs 

 with annular bright condensations inside. There are, however, 

 large, extensive, irregular, and complicated nebulas, which also 

 consist of the three gases, nitrogen ever foremost, though the 

 gases are mixed in difTtrent proportions. The very feeble con- 

 tinuous spectrum which appears in many planetary nebula; can 

 in most cases be shown to arise from the consolidattd nucleus, 

 the fluid or solid central mass. The distribution of brightness 

 in extensive nebulosities is very irregular, and the heat in certain 

 regions rises and falls occasionally a little, though no real altera- 

 tions in the form are known as yet. 



The ray-nebulae are surely mere conglomerations of stars. 

 Those are the long, lenticular nebulae, often so narrow and fine 

 that such an object may rejemble a thin bright line drawn 

 through the nucleus. No such nebula is hitherto known to give 

 a tri-chromatic spectrum. 



It was in 1866 that Secchi commenced to examine red stars 

 with remarkable broad bands in the spectra, and he was already, 

 in 1868, compelled to add a fourth class to his three classes of 

 star-spectra. A systematical search after remarkable star-spectra 

 was undertaken in 1873 and following years in Copenhagen. 

 D'Arrest's four papers in Astronomische Nachrichten contain only 



the most remarkable of those he found, and only such as had 

 not previously been mentioned. That most are above the eighth 

 magnitude is evidently only founded on the difficulty of seeing 

 spectra of smaller stars. 



The circumstance which Secchi remarked in 1868, that yellow 

 and red colours are so often connected with prominent spectra, 

 seems certainly to be of importance, but the many exceptions 

 should warn us from here expecting any great cosmical law. 

 Neither is their connection with variability a rule without excep- 

 tions. There are many strongly coloured stars with very indif- 

 ferent spectra. 



Most of the spectra described are of the third class. These 

 are not uncommon, for when we examine 140 stars we may 

 expect to find one of the third class. They are uniformly dis- 

 tributed over the sky, and found also by white stars. The cha- 

 racter of spectra of this class is constant throughout. The 

 positions of the dark bands were also shown by Vogel, in 1872, 

 to be the same for four bright stars. The columns are generally 

 more distinctly separated towards the red end of the spectrum, 

 though the contrary occurs also, and it is even possible to follow 

 the steps from but finely-indicated bands to absolute discon- 

 tinuity, but the colour has nothing to do with these gradations. 



Still more intimately connected with orange colour is the 

 fourth class, and specimens of this class are, in consequence, 

 very uncommon. D'Arrest ascertained that the dark bands in the 

 s'ar-spectra are formed by groups of compressed dark lines 

 against Secchi's experience. He examined spectra of stars with 

 great proper motion, and found, for instance, the spectra of 

 61 Cygni and 1830 Groomb. to be indifferent, uniform, and con- 

 tmuous. General similarity of the spectra in certain parts of 

 the sky does not exist at all, or has not been proved yet ; for 

 instance, it is not true that red and yellow are wanting ia the 

 spectra of small stars in Orion. W. D. 



THE PROGRESS OF METEOROLOGY^ 



AT the opening of his address Dr. Neumayer regretted that 

 the general knowledge and public appreciation of meteo- 

 rology was still very small in comparison with that of other 

 branches of science. The main object of his address was there- 

 fore to induce his hearers to do all in their power to effect a more 

 perfect and detailed understanding of this branch of science 

 among their countrymen in their respective spheres of activity. 

 He treated the subject, and particularly the weather-forecasts, 

 mainly from his own point of view as a naval officer, and pointed 

 out how desirable a greater interest in marine affairs would be in 

 all circles of German home life. The course which meteorology 

 in its application to daily life has taken may be divided into two 

 categories of observations, first the uninterrupted systematic 

 meteorological investigations, and second, the atmospheric dis- 

 turbances or phenomena governed by the laws of winds, as first 

 described some fifty years ago by Prof. Dove. He then gave a 

 sketch of the progress of meteorology in other countries ; of the 

 establishment of the numerous meteorological stations, and the 

 application of telegraphy to this science ; of the enormous 

 help afforded by the introduction of rapid means of communi- 

 cation. He pointed out how the greatest progress was 

 made by the United States of North America ; that England 

 was second in this respect, and was followed by Holland, 

 France, and Denmark. According to the latest news, the 

 yearly budget for meteorological observations in the United 

 States was raised from 250,000 to 450,000 dollars, apart from 

 all personal expenses. The rise in this sum is explained by the 

 necessity of having special telegraph wires and stations solely for 

 the meteorological service and by the increase in the staff of 

 observers. If in Europe the practical results of observations are 

 not quite as satisfactory as might be desired, it is because the 

 European organisation of the meteorological service is far more 

 imperfect than the American one. The German Government 

 has given its full attention to this important science, particularly 

 with regard to the German navy and the coast population. The 

 poor German fishermen in the Baltic and the German Ocean are 

 already deriving great benefit from the numerous meteorological 

 stations which have been estabhshed along the German coast-line, 

 although it is only eighteen months since the service has begun. 

 The German "Seewarte" has been established and. now performs 

 its share of international work along with the sister-establish- 

 ments of England, Holland, and Prance. Agriculturists will 



I Meteorology in Daily Life. Address delivered at the meeting of the 

 German Association at Munich, by Dr. G. Neumayer, Director of the 

 Deutsche Seewarte at Hamburg. 



