September i8, 1890] 



NATURE 



511 



written with special reference to military and orchestral wind 

 bands. 



In the number of Za Nature for September 6 there is a detailed 

 account of an ingenious application of the properties of iodide of 

 nitrogen to photometry. The photometer, invented by M. Lion, 

 is based on the fact that equal surfaces of iodide of nitrogen, 

 preserved under its mother-liquor, and exposed for equal times 

 to lights of equal intensities, evolve equal quantities of nitrogen. 

 Two vessels are connected by a differential manometer, and 

 when the rate of evolution of the nitrogen is the same in each, 

 the manometer is unaffected. It is stated that the iodide of 

 nitrogen, kept in the mother-liquors in which it has been pre- 

 pared, is perfectly safe to handle. In practice, owing to the 

 difficulty of exactly balancing the two halves of the apparatus, a 

 method analogous to "weighing by substitution" is employed. 

 The accuracy attainable in the measurements is not stated. 

 In the same number another photometer of considerable theo- 

 retical interest is described. It is the invention of MM. Seguy 

 and VerschafTel, and was described by them on September i at 

 the Academy of Sciences, Paris. It is based upon the prin- 

 ciple of Crookes' radiometer, but the disks, instead of being 

 free to rotate, are suspended by a silk fibre, and with an indi- 

 cating needle and divided circle, form a torsion balance. An 

 alum cell is placed in front of the instrument, which, as a 

 photometer, appears to be very sensitive, indicating i-iooth of 

 a standard candle. Moreover, two instruments can be con- 

 structed, which with light of the same intensity give the same 

 readings, an important practical advantage. So long as these 

 instruments are used to compare lights of the same quality, 

 there seems to be no doubt that they can both be made to yield 

 results of practical value, and comparable with each other. It 

 appears doubtful, however, whether the same figure would be 

 obtained with the chemical and with the mechanical photometer, 

 if used to compare the illuminating powers of two sources of 

 light that differed much in character, such as an arc lamp, and 

 a candle flame. 



The additions to the Zoological Society's Gardens during the 

 past week include a Green Monkey ( Cercopithecus callitrichus ? ) 

 from West Africa, presented by Mrs. Roupell ; a Sykes's 

 Monkey {Cercopithecus albigularis ? ) from East Africa, pre- 

 sented by Mr. M. Tanner ; two Bonnet Monkeys [Macacus 

 sinicus (J ? ), a Toque Monkey {Macacus pileaius ? ), two Ring- 

 necked Parrakeets {PalcEornis torquatus) from India, presented 

 by Mrs. Julie Rule ; a Rhesus Monkey {Macacus rhesus ? ) 

 from India, presented by Mr. W. Dodson ; a Grey Ichneumon 

 {Herpcstes griseus (J ) from India, presented by Master Stanley 

 Kerfoot ; a Brush-tailed Porcupine {Atherura africana) from 

 West Africa, presented by the Liberian Government Concessions 

 and Exploration Co., Lt. ; a Common Viper {Vipera bertis) 

 from Hampshire, presented by Mr. W. H. B. Pain ; a Pig- 

 tailed Monkey {Mcuacus nemestrinus <J ) from Java, deposited ; 

 two Vinaceous Turtle Doves {Turtur vinaceus) bred in the 

 Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Objects for the Spectroscope. 

 Sidereal Time at Greenwich at lo p.m. on September i8 = 

 2ih. 51m. 4s. 



Name. 



Mag. 



Colour. 



(i)G.C. 469s 



(2) G.C. 4734 



(3) 75 Cygni ... 



(4) a Aquani 



(5) 9 Pegasi ... 



(6) 249 a Schj. 



(7) R Scuti ... 



R.A. 1890. Decl. 1890. 



Remarks. 



(i and 2) No record has yet been made of the spectrum or 

 either of these objects. The first is described in the General 

 Catalogue as a nebulous star, or a very small cluster ; the 

 second as "pretty bright ; pretty small ; round ; brighter in the 

 middle to a nucleus ; mottled as if with stars ; star south pre- 

 ceding." No very bright nebulae are near the meridian at 

 10 o'clock during the present week. 



(3) The spectrum of this star is a very interesting one of 

 Group II. Instead of the spectrum being totally discontinuous, 

 as in o Herculis and others, the bands 2, 3, 7 are well marked, 

 whilst 4, 5, and 8 are so feeble as to be hardly visible. This 

 species of spectrum has been explained by supposing that the 

 meteor-swarm is still sparse and the carbon radiation con- 

 sequently bright. When the positions of the feeble bands are 

 considered, it will be seen that the explanation is complete. 

 Band 8 extends from about A. 503*5 to A. 496, and this will there- 

 fore be partly masked by the extremity of the brightest carbon 

 fluting starting near \ 517. Bands 4 and 5 both come within 

 the range of the second carbon fluting, starting near A 564, and 

 they also will be partly obliterated when the carbon flutings are 

 wide. None of the other bands, however, will suffer from 

 masking in this way, and they therefore should remain dark. 

 It will be interesting if this explanation can be tested by a 

 direct observation of an unusual width or brightness of the 

 carbon flutings. 



(4) This star has a spectrum of Group III., and may be 

 observed as a study of criteria. 



(5) A star of Group IV. (Vogel). 



(6) This is a typical star of Group VI., showing in addition 

 to the ordinary carbon bands no less than six of the secondary 

 bands, namely 2, 3, 4, 5, 7, and 8. Duner remarks that the 

 two latter are undoubtedly bands, and not lines ; their wave- 

 lengths are 551 and 528 respectively, the latter almost agreeing 

 with E of the solar spectrum. The general spectrum consists of 

 four zones — that is, there is a certain amount of light beyond the 

 carbon band commencing at 474. An observation of the pre- 

 cise character of this band would be interesting ; in comets it 

 sometimes ends abruptly at 474, sometimes fades away gradually 

 on both sides at 468, and sometimes has two maxima, one at 

 468 and one at 474. 



(7) Like S Vulpeculse, referred to last week, this is a variable 

 of comparatively short range and short period, but whereas the 

 spectrum of the former is known to be one of Group II., that of 

 the latter has yet to be determined. Although the period is but 

 168 days, we have not as yet any record of the light-curve of the 

 star, which promises to be an interesting one from the fact that 

 the maximum is stated as 47-57 and the minimum as 6'0-8"5 

 (Gore). If the spectrum be one of Group II. the shortness of 

 the period suggests that the bands should be rather narrow, and 

 this may be made a test observation. There will be a maximum 

 about September 23. A. Fowler. 



The Urania Gesellschaft. — An interesting account of the 

 Urania Institution at Berlin appears in the publications of the 

 Astronomical Society of the Pacific, vol. ii., No. 9. The 

 account was originally written for Prof. Holden by Dr. M. 

 Wilhelm Meyer, the director of the institution. It appears that 

 Prof. Foerster, the director of the Berlin Observatory, first pro- 

 posed the formation of an observatory that should be open to 

 the public, and his proposition was afterwards modified so as to 

 include other branches of natural science. The project was 

 warmly supported by Herr von Gossler, the Prussian Minister of 

 Public Instruction, a grant of land was made, and in March 

 1888 a sort of joint stock company was formed having for its 

 object simply the diffusion of knowledge. The idea having thus 

 taken tangible form, the work of construction was begun. On 

 July 2, 1889, the institution was opened to the public, and at 

 the end of the year had been visited by 60,000 persons. 



The astronomical department has been the main attraction from 

 the beginning. It contains a twelve-inch refractor equatorially 

 mounted, and electrically controlled and illuminated. The in- 

 strument is provided with a filar micrometer, a polarizing 

 telescope, and a complete set of eye pieces ranging in power 

 from 70 to 1300 diameters. Unfortunately neither spectroscopic 

 nor photographic accessories have yet been supplied. Five other 

 telescopes are possessed by the Urania Observatory, viz. a six- 

 inch refractor, a four-inch refractor, a six-inch reflector, a two 

 and a half inch transit instrument, and a comet seeker of five 

 inches aperture. 



NO. 1090, VOL. 42] 



