498 



NA TURE 



[March 24, 1S92 



this month's Knoivledge he describes some observations of 

 changes in appearance of a few variable stars at different epochs. 

 Three variables — T Cassiopeise, R Cassiopeiae, and S Herculis — 

 have been frequently observed as {a) remarkably well defined, 

 almost planetary, disks ; {b) well-defined stars, surrounded by a 

 more or less dense, ruddy atmosphere ; (c) large, woolly, ill- 

 defined images, resembling a small but bright planetary nebula ; 

 ((/) at minimum, in place of the variable, a slight bluish nebu- 

 losity. The changes appear to be real, for stars near the 

 places of the variables have been seen clear and sharp when the 

 haziness of the variables was unmistakable. Other stars with 

 regard to which Mr, Peek has made similar observations are 

 S Cassiopeise, R Tauri, R Auriga:, V Cancri, R Ursse Majoris, 

 S Ursse Majoris, R Camelopardi, R Bootis, S Coronse, R 

 Aquilse, and S Cephei. 



Astronomical Possibilities at Considerable Alti- 

 tudes. — Prof. Pickering, in No. 3079 of the Astronoinische 

 Nachrichten, relates some interesting facts in an article on 

 "Astronomical Possibilities at Considerable Altitudes." They 

 are gleaned from observations made at the Boyden Station of 

 the Harvard College Observatory, which is situated two miles 

 from the city of Arequipa, Peru, in latitude 16° 24' S., and 

 longitude 4h. 45m. 30s. W. of Greenwich, and at an altitude 

 of 8060 feet above sea-level. The air there is so clear and 

 steady that 6 '5 magnitude stars are picked out by the naked eye 

 with great ease, and, when the moon is not too bright, the 

 eleven Pleiads can always be counted. The nebula in Andro- 

 meda forms also a very conspicuous object, "appearing larger 

 than the moon," while, in the 13-inch Clark refractor, "the 

 whole photographic region of the great Orion nebula, first 

 shown in the Harvard photographs of 1887, is clearly visible 

 to the eye," rendering it the "most splendid object in 

 the stellar universe." The steadiness of the atmosphere 

 is also very much remarked there, so much so that a scale 

 of steadiness has been adopted. Some of the brightest stars have 

 been noticed to have as many as six complete diffraction rings 

 round them ; while around these, when the seeing was denomi- 

 nated as "perfect," twelve rings have been counted. "Boiling" 

 was also found to be sometimes completely eliminated, for, in 

 observing bodies of the solar system with a 13-inch and a power 

 of 400, " it was frequently impossible to detect any wavering of 

 the edges of the disk." 



The conclusion that Prof. Pickering comes to with regard to 

 the position of future Observatories is that " moderate altitude is 

 a most desirable qualification," while "for transparent skies 

 one must approach the tropics, and for steady seeing one must 

 have an extremely dry climate." 



Increase of the Earth's Shadow during Lunar 

 Eclipses. — In a memoir with the title "Die Vergrosserung 

 des Erdschattens bei Mondfinsternissen " {Abhandlungen der 

 math. phys. Classe dei- k. Sachsischen Ges. d. Wissenschaften, 

 vol. xvii., Lepzig, 1891), Dr. Hartmann published the results of 

 an investigation into the amount by which the earth's atmosphere 

 increases the diameter of the section of the shadow during a lunar 

 eclipse. An abstract of the memoir appears in the annual 

 report of the Royal Astronomical Society, which has just been 

 issued. Since the time of Tobias Mayer (1750) the coefficient 

 uV has been assumed to represent this increase, although nothing 

 is known as to the manner in which this quantity was determined. 

 Dr. Hartmann has reduced all the observations of lunar eclipses 

 observed independently by several astronomers during this cen- 

 tury, and has deduced the increase of the diameter of the shadow 

 from them. The result of a comprehensive discussion of 2920 

 observations of the contact of the shadow with well-defined lunar 

 formations is, that the increase of the semi-diameter of the 

 shadow is 48" 62 for mean lunar parallax. This corresponds to a 



coefificient of increase = . The ""result may perhaps be 



5079 

 changed 2" or 3" by a discussion cf new, observations, but not 

 more, so it seems desirable that the value of ^V should be used, 

 when required, instead of Mayer's value of -oV- 



THE NEW STAR IN AURIGA. 



"T^HE new star is rapidly getting more and more difficult of 



observation in consequence of its waning light. There is 



very little change in its spectrum, and what change there is is 



not in the direction recorded of Nova Cygni, so it seems pretty 



NO. \ 169. VOL. 45] 



clear that the new body was not a hitherto unobserved nebula 

 to begin with. 



The Astrononiische Nachrichten, No. 3079, contains (at p. 

 109) the following communication from Mr. H. C. Vogel, 

 Director of the Astro-physical Observatory at Potsdam, dated 

 February 29 : — 



"Although the spectroscopic observations of the Nova in 

 Auriga are not yet concluded — since the star will probably con- 

 tinue visible for some time — I consider it of importance, in the 

 interest of the subject, to communicate my observations made 

 hitherto, and the conclusions drawn therefrom, even though the 

 latter should not in the future be confirmed in all points. 



"Concerning, first, the direct spectroscopic observations, I 

 have, on February 20, observed the Nova with a compound 

 spectroscope of a dispersion sufficient just to show the nickel 

 line between the D lines. The hydrogen lines C, F, and H7 

 appeared bright. Their identification was easy by means of a 

 hydrogen tube in front of the slit. These three lines did not 

 exactly coincide with the lines of the comparison spectrum, but 

 were displaced considerably towards the red, without, however, 

 separating completely from the artificial lines, .since they were 

 very broad. The continuous spectium appeared faint, owing to 

 the comparatively high dispersion ; and with certainty only the 

 dark broad F line was recognizable, situate towards the more 

 refrangible side, distinctly separated from the bright line in the 

 spectrum. 



" Between C and F, a large number of bright lines could be 

 seen, but most of them were too faint to be fixed with cer- 

 tainty. In the case of two brighter lines near F, myself and 

 Mr. Frost, who assisted in the observations, succeeded in 

 making very certain wavelength determinations ; we found 

 492'5 /x/^ for the fainter of the two lines, which appeared broad 

 and fuzzy on both edges, and 501 'd ix\x for the brighter line. The 

 limit of error is to be taken at about ± '3 ^^u, and it results from 

 the observation with certainty that the brighter line is not iden- 

 tical with the double line of the air spectrum or with the 

 brightest line of the nebula, and still less the other with the 

 second nebula line. From Young's list of lines most frequent 

 in the chromosphere, it follows that near F only the two groups 

 of lines, soi"87, 5oi"59, and 49344, 492'43, 492*24, 49l"92 

 frequently appear bright. There is no doubt that both lines in 

 the spectrum of the Nova are chromosphere lines, and this result 

 appears to me of great importance, in so far as it is made 

 probable that the line observed in Nova Cygni (1876) — W.L. 

 500 /i/x ± I ii.fj. — which, during the gradual fading of the star, 

 alone remained, was a chromosphere line, and not the nebula 

 line. 



" Further, both myself and Mr, Frost saw probably the mag- 

 nesium lines, certainly the sodium lines bright, as also two lines 

 between b and D, one of which probably was the well-known 

 chromosphere line W.L. 53172, also observed in Nova Cygni. 

 By direct comparison with the hydrocarbon spectrum, the 

 brightest band of which nearly coincides with the b group, and 

 with the sodium flame, b and D were identified. Mr. Frost 

 could see a displacement of the D lines in the star spectrum 

 with respect to the comparison spectrum. There was no in- 

 dication of hydrocarbon bands in the spectrum of the Nova. 



"Up to the present eleven mostly very good spectrographic 

 photographs have been taken ; they were obtained by means of a 

 small spectrograph connected to the photographic refractor of 

 34 cm. aperture. The dispersion is only small, but in the 

 small spectrum of 10 mm. length, extending from F to H, 

 much detail is discernible. The illuminating power of the 

 apparatus is so great, in spite of the narrow slit employed, that 

 even now an exposure of 40 minutes is sufficient to obtain an 

 image suitable for measurement. The bright hydrogen lines 

 F, H7, h, H, and the calcium line Ho, are very broad ; and, 

 as already announced, the corresponding dark lines of a second 

 spectrum are displaced with respect to the bright lines towards 

 the violet, and in spite of the breadth of the latter, are almost 

 entirely separated. There are still some of the hydrogen lines 

 in the ultra-violet visible, but they are too faint for any approxi- 

 mately certain observation. 



" In the last few days the spectrum has changed, inasmuch as 

 in the broad bright lines H7, h, H, and H, (F is only traced on 

 plates which are over-exposed for the middle of the photographic 

 spectrum), two maxima of intensity are plainly discernible, and, 

 as in each of the corresponding dark lines, a narrow bright line 

 has appeared. From the measurements, a connection between 

 these and the hydrogen lines appears beyond doubt, and it is 



