386 



KNOWLEDGE & SCIENTIFIC NEWS. 



[March, 1906. 



ASTRONOMICAL. 



By Charles P. Butler, A.R.C.Sc. (Lond.), F.R.P.S. 



Recent Work on Sunspot Spectra. 



Two importaut papers dealing with the special features of the 

 sunspot spectrum have recently been published. W. M. 

 Mitchell, observing at the Princeton Observatory (which has 

 been rendered notable by the work of Professor C. A. Young 

 on the solar chromosphere and spots), has given a long list of 

 specially aflected lines, an analysis of which confirms the 

 interesting results of previous observers that most of the chief 

 lines concerned are due to the rare elements vanadium, 

 titanium, and some unknown elements. Many of the chief 

 lines were observed as reversed, giving bright centres to the 

 lines. 



G. E. Hale furnishes a long list of lines observed in the 

 spectra of spots photographed with the magnificent equipment 

 lately installed at the Solar Observatory on Mount Wilson in 

 California by the Carnegie Institution. The beautiful illus- 

 trations accompanying the paper will convince many who may 

 still have lingering doubts as to the reality of these specialised 

 phenomena of the sunspot spectrum. In the analysis of the 

 lines observed, the lines chiefly affected are ascribed to 

 titanium; then come lines of manganese, chromium, calcium, 

 iron, nickel, and cobalt. It is specially noticed that all of the 

 lines of silicon in the region examined are much weakened. 

 Many of the •' sput band " lines have been photographed and 

 are identified with faint lines in the Fraunshoferic spectrum. 



Va.riation of the Figure of the Sun. 



From a further examination of solar measurements made 

 b\- Schur and Ambronn with the heliometer at Gottingen dur- 

 ing the period iSgo-igo2, C. L. Poor has obtained more 

 evidence in confirmation of the reality of the variations of the 

 sun's figure which he put forward a short time ago. These 

 later measures cover a whole sunspot period of 11 years, and 

 they show a decided periodicity, the polar diameter being 

 larger in 1S90-1, while the equatorial diameter was greatest 

 durmg 1S92, 1S93, and 1894. The e.xact length of the period 

 is uncertain, but it appears to be nearly the same as the sun- 

 spot period. The amplitude of the variation is about o"'2 ; 

 the difference between the largest positive and negative values 

 being about o"'5. These heliometer measures thus corroborate 

 the conclusions previously determined from Rutherford's 

 photographs, but the amplitude of the variation is much less 

 in the case of the visual observations. 



Ne>v Astrographic Refrak.ctor for 

 Cincinnati Observatory. 



We hear that the Cincinnati Observatory has recently placed 

 an order with Messrs. T. Cooke and Sons, of York, for one of 

 their triple ptiotovisual astrophotographic objectives. The 

 aperture of the new lens will be 9'5 inches, and its local length 

 677 inches, so that one millimetre on the photographic plate 

 will be equivalent to two minutes of arc, this scale being half 

 that of the International Astrographic series of negatives. 



It will be noticed that the ratio of aperture to focal length, 

 or intensity, of the new lens is 1:7, much greater than the 

 usual ratio of i : iS. Moreover it is confidently stated that 

 the objective will give good definition over a field fully 15° in 

 diameter, and so should prove specially satisfactory for photo- 

 graphing comets, nebula, and asteroids. This new photo- 

 graphic equipment will be attached to the tube of the old 

 1 1 -inch refractor, at present mounted in the Mitchell Memorial 

 Building. 



Annular Nebula in Cygnus. 



M. G. Tikhoff has recently communicated to the Comptes 

 Ktiidtis an account of a scries of photographs of nebulae he 

 has obtained at the Meudon Observatory. Some of these show 

 very interesting details of the .Annular Nebula in Cygnuy, 

 N.G.C. 6894. They were taken with a telescope of one metre 

 aperture and three metres focal length, with exposures from 

 2 ' 20'" to j'', on September 27 and October 27, 1900, respec- 

 tively. The nebula is in the form of an elliptical ring with a 

 central condensation. The major axis is about 44"'8, and the 

 minor axis 37"j, It is composed of two rings, an exterior 

 broad one and an inner portion somewhat thinner. On the 

 north-west portion the doubling is interrupted by the presence 

 of the star discovered by Lord Kosse in 1S55. On the outer 

 ring there are several condensations, of which the two 

 strongest are almost opposite the above-mentioned star. 

 Although the general similarity of this nebula to the well- 

 known and brighter Ring Nebula in Lyra is noticeable, it 

 differs in possessing these condensations, while the Lyra 

 nebula is almost uniform in structure; and it is thought that 

 this circumstance indicates a considerable advance of the 

 Cygnian body from the evolutionary standpoint. 



Occultations of Aldebaran. 



On March 2nd and 29th the octultation of the bright yellow 

 star .Aldebaran will offer facilities for several interesting 

 observations. Those possessing small telescopes up to 4 ins. 

 aperture should look specially for the small companion, of 

 about the eleventh magnitude, which is considered a good 

 light test for instruments of this size. It is within 2" of arc 

 in distance from Aldebaran. The other minute attendant 

 star found by Burnham about 31 ""4 distance is not considered 

 to bo physically connected witti the Aldebarian system. 

 At various previous occultations of Aldebaran observers 

 have recorded a slight tendency for projection, or hangiug-on, 

 of the star. Although this might be caused if the companion 

 star were brighter, it is doubtful if it be real, and observations 

 carefully made to solve this question would be welcomed. 



Harvard College Observatory, Report 

 for 1905. 



In his report for the year ending September 30, 1905, Pro- 

 fessor E. C. Pickering has again an enormous amount of work 

 10 record. With the East Equatorial over 13,000 photometric 

 light comparisons have been made by Professor O. C. Wendell, 

 principally with the polarising photometer with achromatic 

 prisms. A large part of these relate to variable stars of the 

 .Algol type, and serve to determine their light curves and times 

 of minima. Measures have been made of four Asteroids, to 

 determine the variation, if any, in their light. Thus from 15S0 

 determinations of Eunomia (15) it appears that this asteroid 

 varies by about half a magnitude in a period of 3'' 24'5't'. 

 With a second photometer, measures have been made of the 

 remarkable variable O Ceti and several double stars. 



With the 12-inch meridian photometer, S1.2S4 settings have 

 been made by the Director, on 148 nights. The measurement 

 of all the Durchmusterung stars in zones 10' wide, at intervals 

 of 5^, has been completed from the North Pole to declination 

 — 20°. 



With the ii-inch Draper telescope, looi plates of spectra 

 were taken, and 133 with the S-inch Draper telescope. The 

 number of photographs taken during the yearis6i6i. Eclipses 

 of Jupiter's satellites and occultations of stars by the moon 

 have been photographically recorded, and work is proceeding 

 with the classification and study ofthe spectra of stars of about 

 the fifth magnitude, during which study many interesting new 

 variables have been detected. 



In connection with modern observatories near, or in, large 

 (owns, a special inquiry has been made with regard to the 

 photographic brightness of the sky. It was found that owing 

 to electric lights, cSic, the sky at Cambridge, Mass., is three 

 times as bright as at points only a few miles distant, and it is 

 suggested that it may be necessary in the future to establish 

 an auxiliary observing station for the northern stars. 



Stellar photographs at .Arequipa were taken with the 13-inch 

 Boyden telescope and the 8-ii;ch Bache, to the number of 2244. 



The Bruce telescope has been in full work, 523 photographs 

 being obtained, of which 27 had an exposure of 4 hours. From 

 a study of these, 1129 new variables have been detected, 909 

 being in the small Magellanic cloud. Other photographs led to 



