468 



NA TURE 



[February 17, 1910 



A SECOND edition of Prof. Willielm Ostwald's " Grosse 

 Manner " has been published by the Akademisclie Verlags- 

 gesellschaft of Leipzig. It will be remembered that the 

 first edition of the work was reviewed at length in our 

 issue of July 29, 1909 Cvol. Ixxxi., p. 121). The price of 

 the volume is 14 marks.. . 



Ol]R ASTRONOMICAL COLUMN. 



Co.MET 1910a. — Reports received from various observers 

 show that at the beginning of . this week comet 19100 was 

 no longer a striking naked-eye spectacle, and there is little 

 that is new to record regarding it. 



Mr. Gustave Gillman" sends us a fine drawing showing 

 the comet's position and tlie extent of its tail as seen by 

 him at .'\guilas, Murcia, Spain,, on January 27 and 31. 

 For the former date the • drawing, which is a large-scale 

 chart of the region of stars wherein the comet was then 

 located, shows, distinctly, the tail extending to f Pegasi, 

 making its length more than 20°; but unfortunately the 

 chart is unsuitable for reproduction here. • 



In La Nature for January 29 (No. 1914) M. Lucien 

 Rudaux describes the comet ' as seen from Paris on 

 January 21 and the succeeding days, and a drawing. shows 

 that it had a brilliant nucleus and a well-developed, tail, 

 several degrees long, . on January 22. A number of 

 observations are also recorded in the Gazette astronomique_ 

 (So. 2b), where attention is directed to the fact that if 

 the apparent length of the tail on January 30 were 30°, 

 the actual length was something like 110 million kilo- 

 metres (68-75 million miles). . 



A number of drawings and photographs of the comet 

 were shown at the meeting of the Royal . Astronomical 

 Society held on February ii. Among other remarkable 

 features were the development of- a shorter tail on the 

 southern edge of the main tail, near the head, and the 

 considerable extension of the main tail at its N.E. 

 extremity; this extension curved quite abruptly from the 

 main axis, and reached nearly to 7 Pegasi. Mr. Hinks, 

 who showed a number of drawings, directed attention to 

 the fact that the bright nucleus was situated on the 

 extreme inner edge of the head, so that the two branches 

 of the tail appeared to enwrap it completely on the sun- 

 ward side. The drawings also depicted the zodiacal light, 

 with which the tail appeared to merge, thus forming a 

 magnificent spectacle. Observations are also recorded in 

 No. 6 of the Comptcs reiidus (February 7). MM. Luizet 

 and Guillaume state that on January 29 and 30 the tail was 

 30° long, and, at a distance of 15° from, the nucleus, its 

 breadth was 2°; on January 31" it was distinctly fainter. 

 MM. Javelle, Charlois, and Schaumasse report that on 

 January 25 the nucleus was round and 10" in diameter, 

 and two aigrettes, , symmetrical with regard to it, were 

 distinctly seen. On February, i the comet was sensibly 

 fainter, and the aigrettes were no longer visible, whilst 

 a further diminution of brightness was recorded on 

 February 2, and the' nucleus was ■ seen to be elongated. 

 M. Borrelly records that on February 3 the side of nucleus 

 nearer the sun was nearly devoid of corria. 



The Magnetic Storm of September, 1909, and Solar 

 Phenomena. — The connection between the magnetic storm 

 of September 25, . 1909, . and the contemporaneous solar 

 phenomena observed at the Meudon Observatory is dis- 

 cussed by M. Deslandres in a paper which appears in 

 No. 2 of the Cotyiptes rendus. A spectroheliogram of the 

 upper hj'drogen atmosphere, on September 24 4h. 3Sm. 

 p.m., shows strong dark filaments connected with the 

 spots, the areas of the latter being greatly diminished. At 

 yh. 3m. a.m. on September 25 these filaments had nearly 

 disappeared, and were broken up, and M. Deslandres 

 connects this phenomenon with that of the magnetic storm. 

 A photograph . of .the ."mean layer " of calcium on 

 September 24 shows the eastern spot to be bordered, on its 

 eastern side, with alternate bright and dark filaments, 

 polygonal in form and sharply defined, and a number of 

 similarly shaped flocculi join the two spots. M. Deslandres 

 names this special structure le riseau chromospherique, 

 and supposes that it shows the region on the western side 

 of the spot to be in a fairly calm state. Photographs 

 taken for that purpose, on September 24, give no evidence 

 NO. 2103, VOL. 82] 



of motion in the line-of-sight, but show the bright vapours 

 above the eastern spot discussed by Dr. Lockj'er. 



M. Deslandres discusses the several theories as to the 

 solar-terrestrial connection, and shows that the " kathode 

 radiation " theory may explain many of the phenomena. 

 The kathode rays leaving the spot are curved, by the 

 exterior magnetic fiv'ld of the , sun, like the spires of 

 nebulfe, and this m.iy account for the mean " lag " of 

 forty-five hours between the meridian-transit of the spot 

 and the incidence of the magnetic storm. The "whirls" 

 of Prof. Hale thus become the effect, rather than the cause, 

 of the magnetic field, which by M. Deslandres 's theory is 

 produced by the corpuscles circulating round the sun with 

 great velocities. The difference between the calcium and 

 hydrogen images is also explained by this theory, for the 

 action of the field would produce different results on atoms 

 of different masses. 



The Intrinsic Light of the Sky. — An interesting 

 method of comparing the intrinsic light of various parts of 

 the sky inter se -and with stars of known magnitude is 

 described by M. Ch. Fabry in. a paper appearing in No. 5 

 of the Comptes rendus (January 31, p. 272). 



In the focal plane of an objective of 48 cm. focal length 

 M. Fabry placed a circular diaphragm of variable aperture.. 

 Passing through this aperture, the light of the sky fell upon 

 an optical system, of ^-is cm. focal length and large 

 aperture, which projected an image of the objective on to. 

 a photographic . plgte. Thus the plate registers, . as a 

 uniformly illuminated circular area, the whole of the light 

 coming from that part of the sky of which the image is 

 fornied behind the diaphragm. In making a determination, 

 two exposures are necessary.: — (i) the camera is directed 

 to a star, e.g. Polaris, and the diaphragm is closed down 

 so that only the light from the star is allowed to reach 

 the Opiate.; ,(2), the camera is directed to. the . region of the 

 sky tobe investigated, and the diaphragm opened so that, 

 an exposure of equal duration will give an image of equal 

 density to that produced in the first case; a simple calcula- 

 tion then gives the ratio between. the intrinsic illumination 

 of the area under consideration and the light of the chosen 

 star. 



By this method M. Fabry finds that a square degree of 

 sky, in galactic latitude 30° and near the pole, gives a 

 photographic intensity equal to 0103 that of Polaris, 

 or 0-02 that of a fifth-magnitude star. The correspond- 

 ing ratios for an area, of one degree square, between /3 

 and 7 Cygnus, one of the brightest regions of the Milky 

 Way, are 0-212 and i-g respectively. These values differ 

 from those obtained by visual observations, probably 

 because the magnitude of Polaris was taken as 2-62, but 

 if the visual magnitude of the latter is taken, 2-12 on the 

 Harvard scale, the result for i square degree of non- 

 galartic sky is 1-46 of a fifth-magnitude star, a value inter- 

 mediate between those obtained by Newcomb (i-i.^) and 

 Burns (2-0). .'\s regards the ratio between galactic and 

 non-galactic sky, M. Fabry's results are in accord with 

 t'ne visual observations. 



Elliptic Elements and an Epiiemeris for Daniel's 

 Comet, iqogc.^From observations made at Rome and Nice 

 on 1909 December 8 and iqio January 2 and 14, Dr. Ebell 

 has calculated elliptic elements for the orbit of Daniel's 

 comet, igoqe, which he publishes, with an ephemeris, in 

 No. 4384 of the Aslronomische Nachrichicn (n. 264I. The 

 elements give 1909 November 28-91228 (Berlin) as the time 

 of perihelion passage, and 6-403 years as the period, but 

 they are not yet considered final. -According to the 

 ephemeris, the comet is now (February 17) 58m. east and 

 38' north of 5 Auriga?, and is only about one-fifth as bright 

 as it was on December 8 ; its daily motion is slightly less 

 than 2m. nearly due east. 



Publications of the Lijnd Observatory, Sweden. — 

 From the Lund Observatory, Sweden, we have received 

 three papers, published as Meddelanden frtin Lunds 

 Astrouomiska Observatorium. No. 5 (series ii.) is by 

 Prof. Charlier, and discusses the motions of the orbit- 

 planes of satellites in various planetary systems. In No. 6 

 M. Henrik Block discusses a class of singularities in the 

 problem of n bodies, and in No. 40 (first series) Dr. Zinner 

 treats of the secular perturbations in the planetary rotation 

 pioblem. 



