376 



NA TURE 



[Feb. i8, i; 



It is the intention of the authorities at the South Kensington 

 Aquarium to endeavour to introduce herrings into the collection 

 of fish now on view there. The difficulty of naturalising this 

 species to artificial existence is very great, as has been proved 

 by former experiments. At sea-port aquaria, however, where a 

 continuity of salt water may be obtained, this difficulty is 

 obviated to a great extent, but at inland aquaria, where the 

 water is seldom changed, it necessitates extraordinary skill to 

 keep them alive. 



At a meeting of the Council of the National Fish Culture 

 Association, held last week, it was stated that the American 

 Government had forwarded another consignment of Salmonids 

 ova since the previous week, and the hatchery was now replete 

 with eggs. It was further stated that the hatchery had been 

 reconstructed and enlarged to meet the strain placed upon its 

 accommodative capacity, so that the Association was in a posi- 

 tion to incubate any number of ova. 



A LARGE supply of salmon and trout ova has been despatched 

 to New Zealand by Sir Francis Dillon Bell, who is most desirous 

 of stocking the waters of that country with Salmonidfe. The 

 ova were obtained by the Tay District Fishery Board, and de- 

 posited in the Howietown establishment until ready for shipment. 

 Much is being done to advance the New Zealand fisheries, and 

 the attempts made in this direction have terminated successfully 

 in nearly every instance. 



The additions to the Zoological Society's Gardens during the 

 past week include a Pennant's Broadtail (Platycercus fennauti) 

 from New South Wales, presented by Mr. H. Stacy Marks, 

 R.A., F.Z. S. ; five Adorned Ceratophrys (Ceratop/trys ormita) 

 from Buenos ;\yres, presented by Dr. F. C. Strutt ; a Common 

 Chameleon (C/iaiihrkon vulgaris) from North Africa, presented 

 by Mr. Charles Kershaw ; a Common Gull [Lants canus), a 

 Black-headed Gull (Lanis ri libiindus), a Kittawake {A'lssn 

 tridactyld), British, purchased. 



OUR ASTRONOMICAL COLUMN 

 Nav.\l Observatory, Washington. — The following novel- 

 ties occur in the programme of work to be pursued during the 

 year 1886 at the Naval Observatory, Washington, recently pub- 

 lished : — 



' ' With the great equatorial it is proposed to make observa- 

 tions of some of the fainter stars in the Pleiades to connect them 

 with the bright ones recently measured with the Yale College 

 heliometer. With the 9-6-inch equatorial observations of variable 

 stars will be commenced. A photometer for this instrument has 

 been ordered from Alvan Clark and Sons ; a spectroscope by 

 Hilger is ready for attachment." 



The Secular Nutation of the Earth's Axis. — M. 

 Folic, having de<luced a periodic formula for the secular varia- 

 tions in obliquity and in longitude, applies the designation 

 secular nutation of the earth's axis to these variations. Defining 

 the normal equator as a plane the inclination of which to the 

 ecliptic of a certain epoch is equal to the mean obliquity of that 

 epoch, and the intersection of which with this latter plane passes 

 at each instant through the mean equinox of that instant, he 

 concludes that, in virtue of the secular nutation of the earth's 

 axis, the mean pole describes round the normal pole, considered 

 as fixed, an ellipse the major axis of which, directed towards the 

 pole of the fixed ecliptic (i.e. the mean ecliptic of the epoch) is 

 sensibly constant during several centuries. The period of the 

 secular nutation is about 30,000 years, differing little from that 

 of the precession on account of the slow motion of the node of 

 the ecliptic, which is only S"7 per annum. Assuming a uniform 

 value of 50" for the secular diminution of the obliquity, M. 

 Folic compares the results obtained from his formula with 

 ancient ob-ervations of the obliquity, and is thus led to announce 

 that the empirical expression f, = - o"-476 -f o" -000018/ for the 

 annual diminution (where t is the number of years from 1850) 

 satisfies very closely the observations from - 250 to -I- 1487. 

 This expression, however, gives a considerably greater variation 



to the secular diminution of the obliquity than that which results 

 from Leverrier's researches. 



Astrophysical Observatory of Potsdam. — The first 

 part of the fourth volume of the publications of this Observatory, 

 which was published in the latter part of last year, contains 

 three papers. The first of these is by Prof. Vogel, and contains 

 the observations which he made with the great Vienna refractor 

 in 1883 for the purpose of testing the performance of the great 

 object-glass. Prof. Vogel's final verdict is altogether favour- 

 able : " The Vienna objective," he .says, "leaves nothing to be 

 desired as regards the precision of the images -, " and he speaks of 

 using with advantage a power even of 1500 upon planetary 

 markings, a statement which is illustrated by a sketch of part of 

 Saturn's ring, as seen with that magnifying power. His prin- 

 cipal observations were, however, spectroscopic. Prof. Vogel 

 utilising the great light-gathering power of the Vienna equa- 

 torial for a detailed examination of the remarkable spectra 

 shown by several faint stars, classified by him under types W.b 

 and III. (5 ; the former including spectra showing both dark and 

 bright lines, and the latter, spectra crossed by dark bands, for 

 the most part sharp towards the red and shaded towards the 

 violet. The bright lines in the former class, with the exception 

 of the green line of hydrogen, have not been identified with 

 those of any element. The principal bands of the latter class 

 Prof. Vogel refrrs, as Dr. Duner does, to the absorption exer- 

 cised by hydrocarbons in the atmosphere of the star. The paper 

 also contains a number of observ.ations of nebula, principally 

 planetary, and is illustrated by four lithographic plates. 



The second paper contains meteorological observations made 

 in tlie years iSSi to 1883, and the third is a very careful investi- 

 gation by Dr. G. Miiller of the influence of temperature on the 

 refraction of light through prisms, of various kinds of glass, of 

 Iceland-spar and rock-crystal. 



Comets Fabry and Barnard. — The brightness of these two 

 comets continues to increase, Fabry's comet in particular pro- 

 mising ere long to be visible to the naked eye ; and it seems 

 probable that at the end of .\pril and the beginning of May we 

 may see the unusual spectacle of two bright comets near each 

 other, and very nearly in the zenith. 



The following ephemerides are given for Berlin midnight, that 

 for Fabry's comet being by Dr. H. Oppenheim, and that for 

 Barnard's by Dr. A. Krueger : — 



Ma 



R A. 



h. m. s. 

 23 21 32 

 23 21 O 

 23 20 27 



■ 23 19 49 



I 59 29 

 I 57 39 

 156 8. 



Fabry^s Comet 

 Decl. 



Loii 



Log. a Bright- 



00370 

 OOI2I 

 9-9860 

 9-9591 



. 27 13-7 N 

 . 28 IO-6 

 . 29 no 

 . 30 14-8 X 



Barnard^ s Cornel 

 . 18 20-1 N. ... 0-2017 

 . 19 20'7 ... 0-1836 

 . 20 23-4 ... 0-1646 



21 28-4 N. ... 0-1443 



. 0-205S 

 0-1958 



, 01836 

 0-1639 



. 0-2412 

 . 02426 

 • 0-2432 

 . 02429 



4-1 



4-8 

 57 

 6-9 



2-9 



3'4 

 37 



Stellar Photography. — The new nebula around Maia, dis- 

 covered by means of the photographs taken at the Paris Obser- 

 vatory, has since been seen with the great Pulkova refractor. 



M. Cruls, Director of the Rio de Janeiro Observatory, has 

 been commissioned by the Emperor of Brazil to have a photo- 

 graphic apparatus constructed similar to that devised by the 

 Brothers Henry at Paris, in order to co-operate with them in the 

 proposed photographic survey of the sky. 



Harvard College Observatory. — Prof. E. C. Pickering 

 has issued his Report for the year 1885. As in former years, 

 chief interest attaches to the photometric researches carried out 

 at the Observatory. With the 15-inch equatorial the photo- 

 metric observations of the eclipses of Jupiter's satellites have 

 been continued. In all, 319 eclipses have now been observed, 

 35 since the end of October 1884. The reduction of the photo- 

 metric observations of the zone stars between the declinations 

 -1-0° 50' and + 1° o' has been carried on, and the observations of 

 DM. stars between + 49° 50' and + 50° o', as well as those 

 between +54° 50' and 4- 55^0', have been completed. These 

 observations have been made with the wedge photometer at- 

 tached to the large equatorial. The resulting magnitudes have 

 been computed by means of the stars occurring in the zones 

 which are also under observation with the meridian photometer. 



