68 



NATURE 



[Nov. 2 1, 1889 



merely a slight hissing. If, however, the mixture has been 

 heated till vapours have begun to make their appearance, the 

 reaction is extremely violent. It is therefore best to allow the 

 contents of the crucible, after fusion, to cool down to a low red 

 heat, when the introduction of the magnesium is perfectly safe. 

 When all action has ceased, the contents of the crucible are 

 again heated strongly, and afterwards allowed to cool until the 

 furnace has become quite cold. On breaking the crucible, all 

 the potassium chloride and the excess of manganous chloride is 

 found to have been volatilized, leaving a regulus of metallic 

 manganese, fused together into a solid block, about three parts 

 by weight being obtained for every two parts of magnesium 

 added. The metal, as thus obtained, is readily broken up by 

 hammering into fragments of a whitish-gray colour possessing a 

 bright metallic lustre. The lustre may be preserved for months 

 in stoppered glass vessels, but, when exposed to air, the fresh 

 surface becomes rapidly brown. The metal is so hard that the 

 best files are incapable of making any impression upon it. It is 

 so feebly magnetic that a powerful horse-shoe magnet capable of 

 readily lifting a kilogram of iron has no appreciable effect upon 

 the smallest fragment. It was noticed that the introduction of a 

 small quantity of silica rendered the manganese still more brittle, 

 and caused it to present a conchoidal fracture, that of pure man- 

 ganese being uneven. The specific gravity of the metal, former 

 determinations of which have been very varied, was found 

 to be 7 '392 1 at 22° C. This number, which was obtained with 

 a very pure preparation, is about the mean of the previous de- 

 terminations. Dilute mineral acids readily dissolve the pul- 

 verized metal, leaving a mere trace of insoluble impurity. It is 

 also satisfactory that practically no magnesium is retained alloyed 

 with the manganese, and the introduction of carbon is altogether 

 avoided by the use of this convenient method. 



The additions to the Zoological Society's Gardens during the 

 past week include a Common Marmoset {Hapale jacchus) from 

 South-East Brazil, presented by Mr. O. Burrell ; a Common 

 Squirrel {Sciurus vulgaris), British, presented by Miss B. 

 Tatham; a Common Stoat (yJ/wj/^/a d-rw/w^a) from Northampton- 

 shire, presented by Mr. Cuthbert Johnson ; a Wattled Crane 

 ■( Grus carunculata) from West Africa, presented by Mr. Robert 

 Sinclair, Jun. ; a Redshank {Totanus calidris) from Devonshire, 

 presented by Mr. R. M. J. Teil ; a White-backed Piping Crow 

 {Gymnorhina leuconota) from Australia, presented by Mr. W. H. 

 Felstead ; a Grey-headed Porphyrio {Porphyrio poliocephalus) 

 from India, presented by Dr. Gerard Smith ; a Common 

 Chameleon {ChanicBleon vulgaris) from North Africa, presented 

 by Mr. G. W. Alder; a Dwarf Chameleon {ChanicEleon pumilus) 

 from South Africa, presented by Mrs. Leith ; a Green Lizard 

 {Lacerta viridis), European, presented by Mr. C. H. Whitlow ; 

 a Common] ay {Garru/us gianda7'ius), European, purchased; five 

 ■Carpet Snakes {More/ia variegata) from Australia, received in 

 exchange. 



OUR ASTRONOMICAL COLUMN. 



Objects for the Spectroscope. 



Sidereal Time at Greenwich at 10 p.m., November 21 = 2h. 

 "3m. 2is. 



Name. 



(i) G. C. 527 ... 



(2) 15 Arietis 



(3) a Arietis 



(4) /3 Trianguli ... 

 <5) DM -f 56° 724 

 (6) R Tauri 



Mag. 



3 



9 



Var. 



Colour. 



Yellowish-red. 



Yellow. 



Bluish-white. 



Reddish-yellow. 



Very red. 



Decl. 1890. 



-1-41 35 

 -f-1859 



+22 57 

 -1-3428 

 -1-5631 

 + 9 55 



Remarks. 



(i) Sir John Herschel's description of this nebula is as follows : 

 — ! Bright, very large, very much extended. The spectrum has 

 not yet been recorded. 



(2) This is a star of Group II., in which Duner records bands 

 2-8, but states that they are neither wide nor dark. The star 

 falls in species 13 of the subdivision of this group, and is 

 well advanced towards Group III. Metallic lines, and possibly 

 hydrogen lines (dark) may therefore be expected. In the earlier 

 stages of the group, no hydrogen lines appear, the radiation from 

 the interspaces between the meteorites being balanced by the 

 absorption of the gas surrounding the incandescent stones ; but 

 in the more advanced members, as in o Orionis, the absorption 

 will probably be found to slightly predominate. The presence 

 or absence of the F line, and of metallic lines, and their relative 

 intensities, should therefore be noted. 



{3) This is a star of either Group III. or Group V., and the 

 U5ual criteria (see p. 20) should be observed in order to deter- 

 mine which. At the same time, the relative intensitic'^ of the 

 hydrogen lines and the metallic lines (say b and D) .'-hould be 

 recorded, so that the star may be placed in a line of temperature 

 with others. 



(4) According to Gothard this is a star of Group IV. The 

 usual observations are required. 



(5) Duner classes this with Group VI. stars, but states that 

 the type of spectrum is a little doubtful. Further observations 

 are therefore required. As the most advanced stars of the group 

 are very red, the colour of this .'^tar indicates that it probably 

 belongs to an early stage of the group, in which the carbon 

 bands would be narrow, and therefore somewhat difficult to 

 observe with certainty ; in that case traces of b and D might be 

 expected. The colour should also be checked. 



(6) Gore gives the period of this variable as 325*6 days, and 

 the range as 7"4-9"o at maximum to < 13 at minimum. The 

 maximum will occur on November 30. The spectrum is of the 

 Group II. type, and belongs to species 9. Duner states 

 that the dark bands, especially 7 and 8, are very wide. In 

 several variables of this class (R Leonis, R Andromedae, &c. ), 

 Espin has observed bright hydrogen lines near maximum, and 

 the question is, Is this common to all the variable stars of this 

 type? As stated with reference to 15 Arietis, under normal 

 conditions the hydrogen lines in the earlier species of the group 

 are absent, because the interspacial radiation balances the ab- 

 sorption ; but if through some cause the temperature increases at 

 maximum, more hydrogen would be driven into the interspaces 

 and radiation would predominate. It may be mentioned that, 

 according to the meteoritic theory, the increase of temperature 

 and luminosity is brought about by the periastrion passage of a 

 secondary swarm through the outliers of the central one. It is 

 not unlikely that slight variations of colour will take place from 

 maximum to minimum, and it is important therefore that the 

 colour should be noted when the spectroscopic observations are 

 made. A. Fowler. 



The Minimum Sun-spot Period. — M. Bruguiere, in 

 U Astronomic, November 1889, gives a series of observations 

 made with a view to determine the exact date of the minimum 

 sun-spot period. The following tables show the condition of the 

 sun's surface with respect to spots from the beginning of January 

 to the end of July of this year : — 



Date, 



Jan. 



3-15 

 18-31 

 8-21 

 2-6 



,. 17-31 

 April 11-30 

 May 1-5 



,, 10-26 

 28-31 



29-30 

 i-u 



25-27 



Feb. 

 Mar. 



June 

 July 



If the small spots that were seen from May 6-9, and also on 

 May 27, be neglected, it will be seen that there would be a 

 period without spots extending from April 11 to June 15— -that 



