254 



NA TURE 



{Jan. 14, 1886 



the brighter portions of comets, and has obtained for 

 many of these bodies hnes which resemble the spectrum 

 of carbon, as taken in a hydrocarbon. 



In Fig. 22 we have, first, the spectrum of Brorsen's 

 comet ; secondlj', the spectrum of Winnecke's comet ; 

 thirdly, the spectrum of carbon in olefiant gas ; fourthly, 

 that of carbon in olive oil. 



More recently the same observer has found other 

 specimens of this class of bodies, which give spectra 

 essentially different from the hydrocarbon type, and he 

 remarks that as the meteors which come down to us differ 

 greatly in chemical constitution, so it i= ot surprising 

 that a similar difference should be found in comets which 

 we know to be very closely allied to meteors. 



Dr. Miller and Mr. Huggins were amongst the first to give 

 us information regarding the spectra of stars. These bodies 

 exhibit spectra very similar to that of the sun— that is to 

 say, they give us an underlying continuous spectrum, in- 

 tersected with darlv lines. We have thus evidence of a 

 similarity in physical constitution between our sun and 

 these very distant bodies. 



The position of the dark lines is the great object of 

 interest in stellar spectra, and by the method already 

 described the presence of various terrestrial elements has 

 been detected in the stars. 



In the most brilliant bluish-white stars, along with the 

 presence of numerous fine Hnes, we have a comparatively 

 small number of prominent absorption lines, the sub- 

 stances which these indicate as present being hydrogen, 

 calcium, magnesium, and sodium. We shall return to 

 this subject on a future occasion. 



Miller and Huggins were so fortunate as to obtain the 

 spectrum of a star which suddenly blazed out in May, 

 1S66, and found in it the unmistakeable presence of bright 

 hydrogen lines. 



Such a star is probably ^to be regarded as exhibiting 

 on an enormous scale the same phenomenon which is 

 frequently seen in the outburst of hydrogen from the 

 interior of our luminary. Indeed, we have sometimes 

 bright lines of hydrogen in the spectrum of certain solar 

 regions. Padre Secchi has also ascertained that several 

 very small stars exhibit bright lines. 



I need hardly say that in the case of the fixed stars 

 where the disc is a mere point, we have no possibility of 

 differentiating between various portions of it, or of ascer- 

 taining the velocities of its atmospheric motions by 

 spectral displacement. 



We have, however, the means of ascertaining by this 

 method whether the star be approaching us or receding 

 from us, and how rapidly it is doing so. Huggins has 

 made many laborious and interesting observations of this 

 nature, and has determined the relative motion to or from 

 us of many stars — a result which could not possibly be 

 ascertained without the spectroscope. 



In Fig. 23 we have an indication of the proper motion 

 of Sirius as seen by the displacement of the hydrogen 

 line F in the spectrum of that star. 



Before concluding this branch of my subject, let me 

 briefly allude to the light thrown by spectrum analysis on 

 the composition of certain of the nebulje. On directing 

 his stellar spectroscope to the planetary nebula in the 

 constellation Draco on 20th August, 1S64, Dr. Huggins 

 found that its spectrum consisted of three bright lines on 

 a dark background — in fine, that it was the spectrum of 

 incandescent gas. 



Of these three lines one is in all probability the hydro- 

 gen line H ; another appears to coincide with one of the 

 lines of nitrogen, while the third does not coincide with 

 any known line. 



Other nebula; have since been found by Huggins to 

 give us similar spectra. 



Fig. 24 denotes the general spectrum given by the 

 nebulas. 



It thus appears that we have already derived great 



information regarding the constitution of the heavenly 

 bodies by means of spectrum analysis. 



Balfour Stewart 

 ( To be continued.) 



NOTES 



The death is announced, in his seventy-first year, of Dr. 

 John Christopher Draper, Professor of Chemistry in the Medica 

 Department of the University of the City of New York. Dr. 

 Draper was the eldest son of the eminent Prof. John W. 

 Draper. His scientific papers, apart from those on the science 

 of medicine, are devoted to chemical and physical subjects ; and 

 amor.g the latter chiefly to optical phenomena. His last one, 

 relating to dark lines in the solar spectrum, attracted some atten- 

 tion at lire time, 1878-79. 



The death is announced of Mr. James Fergusson, F. R. S., on 

 the 9th in^t., at the age of seventy-eight years. Mr. Fergusson was 

 well known by his writings on Indian architecture, and also by 

 his magnificent work on " Tree and Serpent Worship in India." 



The deaths among French Academicians have been unusually 

 numerous of late ; we have to record this week that of M. de 

 Saint- Venant, a member of the Section of Geometry. 



The Russian Academy of Science has elected Mr. David 

 Gill, Astronomer-Royal at the Cape of Good Hope, a Corre- 

 sponding Member. 



Several French papers have published articles on the oppor- 

 tunity of celebrating the centenary of Arago's birth, tliis 

 celebrated astronomer and physicist having been born at Estagel, 

 a country town of the Department of the Pyrenees Orientah", 

 on Feb. 26, 1785. As he was a Copley Medallist and a foreign 

 member of the Royal Society of London, it is expected that this 

 Society will be invited to send a delegate to take part in the pro- 

 ceedings. Arago was elected a member of the Paris Academy 

 at the early age of twenty-three, after having achieved the 

 measurement of the meridian arc from Dunkirk 10 Formentera, 

 for determining the length of the metre. His predecessor was 

 Jerome de Lalande. In 1830 he was elected Perpetual Secre- 

 tary, and he continued to act as such during twenty-three years 

 up to his death, which took place in 1853. His works have 

 been edited by Barral, and fill seventeen large octavo volumes, 

 of which four are devoted to " Astronomie Populaire." 



In a very excellent article va Science an. " l^Mt Government 

 and its Scientific Bureaus," we find some wholesome remarks un 

 tlie conditions under which scientific work can be performed at 

 its best. " Science cannot be carried forward by prescribing too 

 definitely the tasks of scientific men. They may be bound Ly 

 appointed days and hours ; they may be told to perform specific 

 duties, — and if only the maintenance of routine work is required, 

 such regulations may secure fidelity and efficiency. But if know- 

 ledge is to be advanced, if better methods of work are to be dis- 

 covered, if greater accuracy is desired, if unknown facts are to 

 be ascertained and recorded and discussed, and, in short, if there 

 is to be real progress, the methods of freedom are to be em- 

 ployed, not those of petty regulation. By this we mean that if 

 the great undertakings which the Government has in charge, if 

 especially its surveys of the coast and of the interior are to go 

 forward, discretion must be given to the chiefs of bureaus, and 

 they must be held to accountability for the aggregate succes- of 

 their work. Honesty, economy, clear and accurate statemeni 

 of accounts are, of course, to be demanded in every office : 

 nobody questions this. But the determination of what shall be 

 Undertaken in a given year, to whom it shall be assigned, what 

 allowances shall be made for instruments, books, and assistants, 

 —these are questions which experience and judgment must 

 decide. Somebody who has all the facts in mind must make 



