AtlgUSt 22, 1889] 



NATURE 



407 



nesium fluting at 500," really at 5006 "5, yet I thought it desirable 

 to undertake the laborious task of comparing, with the necessary 

 caie and precautions, the nebular line directly, in the spectro- 

 scope attached to the telescope, with the spectrum of burning 

 magnesium. 



Arrangements were made by which the light from burning 

 magnesium was thrown into the telescope from the side and then 

 reflected down, under conditions similar with the light from the 

 nebula, upon the slit of the spectroscope. By this arrangement 

 any flexure in the tube connecting the spectroscope with the 

 telescope would affect both spectra alike. The coincidence in 

 position of the spectrum from burning magnei-ium with that of a 

 heavenly body to which the telescope was so directed that its 

 light fell upon the slit of the spectroscope, was tested with great 

 care on several occasions by comparing the three bright lines of 

 magnesium with the corresponding lines, l)^, b^, b^, in the spec- 

 trum of the moon. Indeed, to prevent any possible error in the 

 observation of apparent want of coincidence of the nebular line, 

 if the light from the burning magnesium should by an accident 

 so come upon the slit as to bring its spectrum in a very minute 

 degree on the less refrangible side of its true position relatively 

 to the nebular line to be observed with it, the arrangement was 

 purposely made that the lines of magnesium were seen to fall 

 upon the corresponding dark lines at b in the moon, a very little 

 on the more refrangible side of the middle of those lines. This 

 state of things would diminish a little the interval which should 

 be seen between the nebular line and the edge of the magnesium- 

 flame band, and so make the determination more difficult ; but 

 if under such circumstances the nebular line was seen on the 

 more refrangible side of that of magnesium, the observation 

 would be much more trustworthy, for in the case of coincidence 

 with magnesium the line would have appeared towards the 

 opposite and less refrangible side of the magnesium line, 

 broadening the magnesium line on this side. I considered that 

 the comparison could be made most satisfactorily by the com- 

 plete superposition of the two spectra, that from burning magne- 

 sium l)eing gradually reduced in brightness by the interposition 

 of coloured glass screens, until the ground of tie spectrum 

 between the successive bright lines of the band of the magnesium- 

 flame spectrum was sufficiently subdued to alow of the nebular 

 line being seen upon it. 



Under these circumstances, if the nebular line had the posi- 

 tion which my direct comparisons and the micrometric observa- 

 tions of other observers assign to it, it would be seen as a bright 

 line at a very small interval within the line ending the band, 

 and to the observer the band would appear to commence with a 

 double line. 



This direct comparison was first successfully made on March 

 6, 1889. The observations were made with the 15" refractor 

 belonging to the Royal Society. The spectroscope used has 

 two compound Grubb prisms, each with 5 square inches of base, 

 and giving nearly twice the dispersion of a single prism of 60°, 

 namely, 9° 20' from A to H ; and collimator and telescope of 

 I ■25- inch aperture. An eye-piece magnifying eighteen times 

 was employed. The nebular line was brought upon the cross- 

 wires, and when carefully focussed and clearly seen, the light 

 from burning magnesium was thrown in. This observation is 

 one of great difficulty, especially as the interval to be observed 

 had been purposely reduced by causing the magnesium to fall, 

 for the sake of the greater trustworthiness of the observations, 

 on the more refrangible s de of its true position. Although I 

 consider the results to be satisfactory, I prefer to say that I, and 

 Mrs. Huggins independently, believed fully at the time that we 

 saw the appearance which all former observations of this line 

 led me to expect — namely, the nebular line to fall within the 

 termination of the magnesium band, and to form with the band- 

 boundary a double line. The relative positions of the two 

 spectra are represented in diagram across the page. The line 

 at the end of the luagnesium band was then brought upon the 

 cross-wires, without any attention being given to the nebular 

 line ; when the burning magnesium went out, the nebular line 

 was seen to be at a measurable distance to the left of the inter- 

 section of the wires — namely, on the more refrangible side. 



When the object glass of the telescope was covered, the mag- 

 nesium band presented its usual appearance — namely, terminat- 

 ing in a single line. These comparisons were repeated and 

 confirmed generally on March 9, March 11, and March 16. 

 On March 9 a single s-uccessful comparison was made with a 

 more powerful sp^ ctroscope, giving a dispersion equal to nearly 

 eight prisms of 60°. [Comparisons have been made since with 

 the planetary nebula in Hydra. The short line of the nebula 



was found to fall within the termination of the magnesium band 

 at about the small distance which corresponds to the known 

 position of the two lines. — A pri/ z6.] On all these nights the 

 comparisons were repeated independently and fully confirmed 

 by Mrs. Huggins. 



These comparisons can be successfully imitated in the labor- 

 atory by directing a spectroscope of sufficient power to the line 

 of lead which the nebular line is sufficiently near, the slit being 

 narrow, and the electrodes of lead near each other ; and then 

 causing, with the necessary precautions, the light of burning 

 magnesium to fall also upon the slit. The lead line will be seen 

 to fall within the end of the band, and to form with it a double 

 line. 



It may be mentioned in this place that this line of lead, and 

 the iron line at 4957 at the position of the second nebular line, 

 can be conveniently used in the laboratory in any chemical re- 

 search on the nature of the nebulae. No terrestrial line which 

 does not fall almost exactly at these positions in the spectrun* 

 can have any claim to further consideration. 

 ( To be continued. ) 



Paris. 

 Academy of Sciences, August 12. — M. Des Cloizeaux, 

 President, in the chair. — Remarks in connection with the " In- 

 troduction a I'etude des Races humains," Part II., presented to 

 the Academy by M. A. de Quatrefages. In this second part the 

 author passes from the general questions touching the evolution 

 of man to those touching the evolution of the human races, of 

 which he reckons at least one hundred and seventy- two, exclu- 

 sive of minor varieties, all however reducible to the three 

 fundamental black, yellow, and white stems. Adhering to the 

 natural method of classification, as understood by Jussieu and 

 Cuvier, he divides these stems into btanches corresponding to 

 primary and secondary divisions, under which come the ya:^;/?'^^ 

 arid groups. Much stress is laid on the early migrations of man, 

 resulting in crossings of all sorts, and the general displacement 

 of pure by half-caste races. The position of fossil man In the 

 general scheme of classification is also studied, the five or six 

 known varieties discovered in Europe being divided into two 

 distinct branches allied to the white stock. Two distinct 

 Quaternary types are also recognized in America, that of the 

 Pampas affiliated to the Siberian, and that of the Lagoa Santa 

 to the Eskimo branch of the yellow stock. Some bold specula- 

 tions are indulged in regarding the primaeval homes of the three 

 fundamental groups and their subsequent dispersion from com- 

 mon centres over the face of the globe. In this scheme the 

 north of Asia is considered the cradle of mankind, whose three 

 primary divisions grouped themselves round the great central 

 tableland, whence they gradually spread over the continents 

 during Tertiary and Quaternary times. In the Oceanic world 

 the Eastern Polynesians are affiliated to the white, the Melane- 

 sians (Papuans) to the black, and the Malays to the yellow stock, 

 each division migrating from the mainland in the order already 

 indicated by Prof. Keane (" Indo-Chinese and Inter-Oceanic 

 Races and Languages"). The work is illustrated with 441 

 figures inserted in the text, four plates, and seven maps. — On a 

 general law of induction in circuits devoid of resistance, by 

 M. G. Lippmann. In this study the author proceeds exactly as 

 in rational mechanics, where the fundamental laws are estab- 

 lished, apart from the disturbing element of friction, which is- 

 afterwarcls considered as a particular force. He seeks the most 

 general law of induction by assuming resistance to be null, and 

 justifies this procedure a posteriori by the simplicity of the results, 

 by their easy application and agreement with recent experiments. 

 — On the vascular apparatus in animals and plants, studied com- 

 paratively by the surgical and thermochemical methods, by M. 

 Sappey. In previous communications the author showed that 

 in the vertebrates the thermochemical method is not only useful 

 but preferable to the older process for the study of certain organs, 

 especially the harder parts. In the present paper he directs 

 attention to the structure of the vascular apparatus in plants and 

 animals studied both by the surgical and thermochemical 

 methods. The latter process is shown to yield as complete, 

 accurate, and satisfactory results as could be desired ; it is un- 

 questionably superior to the former in the analysis of the veins 

 and arteries of animals, and of the woody and other vt ssels of 

 plants. — The virus of diphtheria, by M. C. H. H. Spronck. 

 The author communicates the results of the researches on human 

 diphtheria made by him, jointly with MM. Wingtens, Van dtn 

 Brink, and Van Herwerden, in Utrecht. The disorder is studied 

 chiefly in connection with its action on the region of the kidneys. 



