NATURE 



[June 5, 1890 



Lord Rosse observed a longitudinal rift, but this has not been 

 confirmed by later observations. According to Dr. Huggins, 

 the spectrum is continuous, but it is not at all unlikely that 

 further observations may show that it is not entirely so. The 

 whole nebula appears to resemble that in Andromeda, even to 

 the dark rift, and we now know that the spectrum in that case is 

 not perfectly continuous. Intending observers of this class of 

 nebula spectra will do well to examine the spectrum of Comet 

 Brooks, which was referred to in last week's notes. The spec- 

 trum of the comet is apparently continuous at first sight, but 

 careful observation shows beyond question the existence of the 

 usual flutings of carbon. These flutings may also be expected 

 in the nebulae having so-called "continuous " spectra. 



(3) D' Arrest likens the spectrum of this star to that of 3 

 Pegasi, but Duner thinks it more like o Herculis. All the 

 bands 1-9 are very strongly marked, and are wide and dark. 

 Observations similar to those suggested for other stars of the 

 group are required. 



(4) According to Vogel, this star has a well-marked spectrum 

 of the solar type, but Duner classes it with stars of Group II. 

 He states that the bands 1-8 are seen, but that they are narrow 

 and not very dark, 4 and 5 appearitig as lines. He also suggests 

 that the spectrum is an intermediate one between Group II. and 

 Group III. As I have pointed out on previous occasions, it is 

 these intermediate stages which require a detailed study. It is 

 pretty certain that the passage from one group to another will 

 not be abrupt, but that there will be intermediate stages between 

 each successive two. The star in question is probably slightly 

 less advanced in condensation than Aldebaran. 



(5) This is a star of Group IV. (Konkoly), but in addition to 

 the hydrogen lines, D and /; are distinctly visible. The usual 

 observations are required. 



(6) The range of this variable is from 6-o-8'i at maximum to 

 1 3 "2 at minimum, in a period of about 302 days. The increase 

 of light is very rapid, whilst the decrease is slow and irregular 

 (Sawyer). The spectrum is a fine one of Group II., the bands 

 1-9 being wide and dark ; 7 and 8 are especially remarkable 

 (Duner). The usual bright lines which are now expected to 

 appear at the maxima of stars of this class should be looked 

 for. The maximum will occur about June 12. 



A. Fowler, 



Actinic Light of the Solar Corona. — Prof. Frank H. 

 Bigelow, in Bulletin No. 15 of the United States Scientific 

 Expedition to West Africa, dated April 19, 1S90, gives an 

 interesting note on the law of distribution of the actinic light of 

 the solar corona. His paper on " The Solar Corona, discussed 

 by Spherical Harmonics," noted in Nature, vol. xli. p. 595, 

 assumed that the surface distribution of the electro-magnetic j 

 potential was expressed by C cos %, the constant representing \ 

 the maximum, and Q the angular distance from the coronal pole ; j 

 the visible lines of the corona being shown to coincide in direc- 1 

 tion with the lines of force generated under these conditions. It 

 is now suggested that the corresponding equipotential lines j 

 denote the position and direction of the surfaces of iso-actinism 

 as referred to the same pole, or, in other words, that the actinic 

 brightness is directly proportional to the potential. From the 

 discussion it follows that the poles become the critical points for 

 examination as to the actinic intensity of the corona ; the sky in 

 the neighbourhood should also be examined with great care ; 

 these two results, combined with the visible linear distance of 

 the contour of merging of the polar rays in the sky light, in 

 terms of the radius of the sun corrected from the covering lunar 

 disk whto taken in combination with the formula for these 

 surfaces, will enable the whole of the coronal light to be 

 discussed as simple phenomena. 



On THE Rotation OF the Sun. — Prof. N. C. Duner has 

 made a series of observations of the displacement of Imes in the 

 spectrum at the eastern and western edges of the sun for the 

 purpose of deducing the time of rotation {Aslr. Nach., 2968). 

 The observations were made from 1887-89 with a Rowland 

 grating spectroscope of high power attached to the refractor of 

 Lund Observatory, the distances between several lines in the a 

 group of the solar spectrum at opposite edges of the sun being 

 micrometrically determined. The results of the measure? are 

 given in the following table, where ^ is the heliocentric latitude 

 of the points on the sun's edge, v the velocity in kilometres with 

 which the point on the edge approaches the earth, | the anjle 



of rotation in 24 hours, and n the number of measures made in 

 the different years : — 



These values of |, deduced from spectroscopic observations, 

 show that the equatorial zone of the solar surface has a shorter 

 time of rotation than zones in higher latitudes, the results agree- 

 ing with those found from sun-spot observations. The advantage 

 of the method used by Prof. Duner, however, lies in the fact 

 that it allows observations of rotation to be made in the neigh- 

 bourhood of the poles. A comparison of the spectroscopic and 

 the spot observations shows that the former gives a slightly 

 smaller velocity of rotation than the latter. 



It may be remembered that the work done under the direction 

 of Prof. Rowland at Baltimore showed that "the absorbing 

 layer of gases by which the Fraunhofer lines are formed does 

 not behave like the sun-spots, but is slightly retarded at the 

 sun's equator." 



PuLKOVA Observatory. — The magnificent volume issued 

 in commemoration of the jubilee of the Pulkova Observatory 

 has been received. In the volume an account is given of the 

 30-inch refractor and the Astro-physical Laboratory, and the 

 twelve plates which illustrate it are worthy representations of an 

 enviable reality. It is hardly necessary to say that the history 

 of the Observatory is fully delineated, and that technical descrip- 

 tions of the instruments are given, whilst Hermann Struve gives 

 a long account of the determination of the instrumental constants. 

 A resume is also given of the work done in the Astro-physical 

 Laboratory, and a comprehensive bibliography of the various 

 astronomical, geodetical, and other studies that have been 

 completed. Indeed, the whole of the splendidly finished work 

 is a fitting memento of the jubilee that it celebrates. 



Telluric Lines of the Solar Spectrum. —M. J. Jans- 

 sen presented a note to the Paris Academy, on May 27, relative 

 to some results he has obtained during a stay in Algeria, where 

 he has been for about four months investigating the action of 

 the atmosphere on the solar spectrum by means of photographs 

 taken when the sun is on the meridian and horizon. The photo- 

 graphs were taken with the aid of a Rowland's grating, and iso- 

 chromatic plates were used in order to obtain records of the 

 less refrangible portions of the spectrum. The work is not yet 

 finished, but M. Janssen notes that, without the purity of the 

 heavens in Algeria and the continuance of favourable days, it 

 would have been impossible to obtain any results. 



Brooks's Comet {a i89o).^The following ephemeris com- 

 puted by Dr. Bidschof is given in Astronomische NachrichUn, 

 No. 2969 : — 



1890. 



R.A. 



June 4... 18 56 29 



NO. 1075, VOL. 42] 



5- 



6... 



7... 



8... 



9... 

 10.., 

 II .. 



12 ., 



'3 •• 



14.. 



15- 

 16.. 

 17.. 

 18.. 

 19.. 



48 o . 

 39 9 • 

 29 54 ■ 

 20 17 . 



10 20 . 

 o 3 • 



17 49 30 • 

 38 44 • 

 27 48 . 

 16 44 . 

 ■5 37 • 



16 54 31 • 

 43 29 . 

 32 35 • 

 21 53 



11 25 . 



Decl. 



.-1-60 468 

 . 61 287 

 . 62 7-9 



• 62 44-3 



. 63 17-8 



. 63 48-1 



• 64 151 

 . 64 387 

 . 64 58-6 



.. 65 14-8 



.. 65 27-5 



.. 65 36-6 



.. 65 42-1 



.. 65 440 

 65 42-6 



•■ 65 377 



■• 65 29-5 



Log r. 



Log ^. 



B right - 



0-2816 ... 0-1958 ... 3-57 



3-2820 



1978 



3-53 



•2827 ... 0-2027 ... 3-44 



... 0-2837 ••■ 0-2102 ... 3-31 



0-2849 ... 0-22C0 ... 3-15 



The brightness at discovery has been taken as 



unity. 



