July 24, 1890] 



NATURE 



303 



Wharton ; a Snow Bunting {Phctrophaties nivalis), European, 

 presented by Mr. J. Young, F.Z.S. ; a Common Boa {Boa 

 <:onstrictor) from Venezuela, presented by Mr. R. J. Money ; a 

 White-thighed Colobus {Colobus velUrosiis <J) from West Africa, 

 a Cape Ratel {MeUivora capensis i ) from South Africa, an 

 Arctic Fox {Canis lagoptis ? ) from the Arctic Regions ; four 

 Spoonbills {PlataUa leucorodia), European, a Short-toed Lark 

 {CalendreUa brachydactyla i) from Algeria, purchased; four 

 Australian Wild Ducks {Anis superciliosa), two Slender Ducks 

 {Anas gibherifrons), eight Chilian Pintails {Dafila spinicattda), 

 six Summer Ducks (^j: sponsa), four Mandarin Ducks {^^x 

 gakriculata), two Red-crested Pochards {Fuligula rufina), bred 

 in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



Objects for the Spectroscope. 



Sidereal Time at Greenwich at lO p.m. on July 24 

 i8h. lom. 17s. 



Remarks. 



(i) This small bright nebula was thought by W. Struve to be 

 one of the most curious objects in the heavens. The G.C. 

 description is : "A planetary nebula ; very bright ; very small ; 

 round ; a little hazy." According to D'Arrest, its diameter is 

 about 7". The observations of Dr. Iluggins and Captain 

 Herschel show that the spectrum consists of the three chief 

 nebula lines, and a faint continuous spectrum. Dr. Huggins 

 alfo notes that "the lines are exceedingly sharp and well- 

 defined." This latter observation requires confirmation, and 

 the spectrum should also be examined for other lines, as we 

 know that a greater number of lines are seen in other nebulae of 

 the same class. 



(2) This is the so-called " Horse-shoe Nebula," which is thus 

 described by Herschel : "A very remarkable object ; bright ; 

 extremely large; extremely irregular figure; 2hooked." The 

 spectrum has been observed both by Dr. Huggins and Captain 

 Herschel. The former noted in 1866 that the line near A 500 

 was visible, in addition to a faint continuous spectrum, and 

 added : " When the slit was made as narrow as the intensity of 

 the light would permit, this bright line was not so well defined 

 as the corresponding line in some of the other nebulae under 

 similar conditions of slit, but remained nebulous at the edges." 

 It will be seen that this observation gives the chief line a very 

 different character to the preceding one (4390), and it is very 

 desirable that the discrepancy should be cleared up, especially 

 as Dr. Huggins has recently stated that the line is always seen 

 sharp and well defined, although there is no evidence to show 

 that he has reobserved the nebulae in which he formerly recorded 

 it as ill defined. It is important that both nebulae should be 

 examined as nearly as possible at the same time with the same 

 instrumental conditions. Captain Herschel simply writes : 

 "Bright object ; bright lines." 



(3) The spectrum of this star is one of great interest in con- 

 nection with the view that stars of Group II. are similar in 

 constitution to comets. Duner states that, notwithstanding the 

 small magnitude of the star the bands are very well seen even in 

 the ultra blue, and that they are so wide and dark that the spec- 

 trum is totally discontinuous, especially in the blue-green and the 

 blue. Now it seems pretty evident that all the light referred to 

 in the blue in a faint star like this cannot be due simply to con- 

 tinuous spectrum, and it is therefore probably due to the radia- 

 tion of some substance. This substance is probably carbon, 



NO. 1082, VOL. 42] 



giving a series of bright ilutings in the blue-green and blue, and 

 giving rise to apparent dark bands, which are in all probability 

 simply the dark spaces between the bright flutings. The mea- 

 surements made by Duner and Vogel of the bands in other stars 

 show close coincidences with the carbon flutings, but the ques- 

 tion can only be finally decided by direct comparisons. If the 

 existence of the carbon flutings be confirmed, then we must 

 conclude that stars of Group II. and comets showing the same 

 series of flutings are identical in constitution. 



(4 and 5) These are stars of the solar type and of Group IV. 

 respectively, and the usual more detailed observations are 

 required in each case. 



(6) The observations of Secchi and Duner show that the 

 spectrum of this star is a well-marked one of Group VI. ; but 

 the only details observed were three " zones" separated by two 

 strong dark bands. P'urther details and deviations from the 

 regular type should be looked for. A. Fowler. 



Nice Observatory. — The third volume of the "Annales 

 de rObservatoire de Nice " contains a new map of the solar 

 spectrum by the late M. L. ThoUon, the whole of the theory of 

 the minor planet Vesta by M. Perrotin, the Director of the 

 Observatory, and numerous observations of comets and planets 

 made by M. Charlois. 



The part of the spectrum mapped by M. Thollon extends from 

 A to b, and is contained on seventeen beautifully engraved plates, 

 each having two horizons 32 cm. long. The whole length is thus 

 a little over ten metres, and the number of lines contained in it 

 is about 3200, of which 2090 are said to have a solar origin, 866 

 are purely telluric, and 246 have a mixed origin — that is to say, 

 they result from the superposition of solar and telluric lines. 



Each of the 33 horizons is divided into millimetres, from 

 o to 320, hence the lines can easily be read off to ^^ of a division. 

 Thollon intended at the beginning of his work to express the 

 position of the lines on a scale of wave-lengths, and this would 

 doubtless have facilitated their identification to a considerable 

 extent ; but the method of relative measurement which he 

 adopted was more accurate than the absolute measures made 

 by Angstrom, and he found that to use a wave-length scale it 

 would be necessary to alter a number of accepted places of lines 

 or to alter his measured intervals. It is rather unfortunate that 

 such should be the case, for ready reference to the lines and 

 comparisons of them with those mapped by other observers are 

 rendered somewhat difficult. Beneath each scale are four 

 horizons on which are respectively represented : (i) the appear- 

 ance of the lines when the sun is 80° from the zenith and the air 

 is dry ; (2) the appearance of the lines when the sun is 60' 

 from the zenith and the air is very moist ; (3) the appearance 

 of the lines when the sun is 60° from the zenith and the air is 

 very dry ; (4) the lines of solar origin— that is, those that would 

 be observed from outside our atmosphere. The width of the 

 lines was determined for each of the four horizons, and intensities 

 are expressed from I to 10, i indicating the weakest and 10 the 

 strongest lines. The values for each line are given in the text 

 relating to the maps. Another horizon gives the position of iron 

 lines, but this is incomplete in some ol the maps owing to M. 

 Thollon's death. 



The theory of Vesta, by M. Perrotin, is in continuation of 

 that published in the first volume of " Annales de I'Observa- 

 toire de Toulouse, 1880," and deals with the algebraical expres- 

 sions of the perturbations produced on its elements by different 

 planets. 



Enlargement of Photographs of Stellar Spectra. 

 — The enlargement of all the photographs of stellar spectra 

 taken under Prof. Pickering's direction at the Henry Draper 

 Memorial observatories is made by means of a cylindrical lens, 

 and the result of the adoption of this method is well known. 

 Dr. Scheiner, of Potsdam Observatory (Astronomische Nach- 

 richten. No. 2969), has obtained even better results by fixing 

 the negative lengthways in a frame which has a to-and-fro 

 movement. The motion causes the width of the lines to be 

 increased on the plate being exposed, in a manner similar to 

 the increase that takes place when a cylindrical lens is inserted 

 between it and the negative. The advantage of the arrange- 

 ment over that of Prof. Pickering lies in the fact that the 

 diminution of the intensity of the lines in the process of 

 enlargement is much less. 



The method now described by Dr. Scheinr r has been used 

 successfully at South Kensington for some time. 



