2l6 



NA rURE 



[June 27, 1901 



generated is closed either with an ordinary cork or with an india- 

 rubber stopper, and, with the object of arresting seleniuretted and 

 sulphuretted hydrogen, the gas, as it passes from the flask to the 

 mirror-tube, is brought in contact with lead acetate solution, 

 sometimes bubbled through the liquid and sometimes passed 

 through cotton-wool or over a roll of filter-paper saturated with 

 the solution. Where cork has been in contact with arseniuretted 

 hydrogen there is danger of sufficient of the arsenic compound 

 being retained by this porous substance to render its continued 

 use a possible source of error ; with rubber there is always the 

 chance that arsenic or antimony may be present as one of the 

 constituents of the material, and as regards the use of lead 

 acetate it has been urged that to bubble the gas through a small 

 quantity of the solution is safer than to pass it through or over 

 cotton-wool or filter-paper. The apparatus sent us has been 

 designed to avoid the use of a cork or rubber stopper, and to in- 

 clude a convenient means of passing the gas through a minimum 

 quantity of lead acetate solution. To a wide-necked flask of 

 200 c. c. capacity is fitted a hollow glass stopper, perforated by 

 the gas-exit tube, which supports a bulb containing a small 

 quantity of lo per cent, acetate of lead solution. The stopper 

 is ground to fit tightly into the neck of the flask, and as the gas 

 passes up the exit-tube it bubbles through the lead acetate solu- 

 tion in the bulb and so on to a calcium chloride drying-tube, to 

 which is attached the mirror-tube in which the arseniuretted 

 hydrogen is decomposed. The apparatus is neat and effective. 



The additions to the Zoological Society's Gardens during the 

 past week include three Derbian Wallabys (Macropus derbiamis, 

 i 9 and juv. ) from Australia, presented by Captain Ben Jones ; 

 a King-tailed Coati (A'rt«(a)V(/ij) from South America, presented 

 by Mr. Thomas Mackenzie ; an Egyptian Jerboa (Dipus 

 aegyptius) from North Africa, presented by Mr. J. Manuel ; an 

 Active Amazon (Chrysalis agilis) from Jamaica, presented by 

 Mrs. V. A. Taylor ; a Darwin's Rhea {Rhea darwini) from 

 Patagonia, presented by Mr. \l. F. Fox ; a Large-billed Weaver- 

 Bird (Ploceus tiicgar/iynclius, i ) from Naini Tal, deposited ; a 

 Baya Weaver-Bird (Ploceus haya, i ), two Black-throated 

 Weaver-Birds (Floceits atrigiilaris), a Black-headed Finch 

 (Mtinia malacca), a Chestnut-bellied Finch (Muniartibro-nigra), 

 two Hybrid Finches (between Mtinia malacca and M. rubro- 

 }iig}-a) from India, presented by Mr. Frank Finn ; two Bennett's 

 Wallabys (Macropus beiiiieiti) from Tasmania, a Black Wallaby 

 (Macropus iialabalus) from New South Wales, a Ring-necked 

 Parrakeet (Pataeornis lonjuala) from India, an August Amazon 

 (Chrysalis augusla) from Dominica, fourteen Algerian Skinks 

 (Eiiiiteces algeriensis) from North-west Africa, a Derbian Sterno- 

 there (Sternothaerus derbiamis) from West Africa, three Simony's 

 Lizards (Lacerla simoiiyi) from the Canaries, eight Three- 

 streaked Skinks (Mabuia Iriviltata), two Streaked Skinks 

 [Mabiiia vittata), a Hissing Sand Snake (Psammophis 

 sibilaus) from Syria, four Grey Monitors ( Varanus griseus), 

 five Common Skinks (Scinciis officinalis), four Ocellated Sand 

 Skinks (Chalcides ocellalus), six Turkish Geckos (Heinidaclylus 

 inabouia) from Western Asia, deposited ; an Axis Deer (Cervus 

 axis, i ) from India, purchased ; six Silver Pheasants (Etiplo- 

 camus nycthemerus), four Gold Pheasants (Thaumalea picla), six 

 Common Pheasants (Phasianus colchicus), bred in the Gardens. 



OUR ASTRONOMICAL COLUMN. 

 Astronomical Occurrences in July. 

 July I. 9h. Jupiter in conjunction with moon. Jupiter 

 3° 42' S. 



1. igh. Saturn in conjunction with moon. Saturn 



3° 36' S. 



2. 9h. 29m. to 9h. 47m. Moon occults B.A.C. 6710 



(mag. 6'0). 



NO. 1652, VOL. 64] 



July 3. iih. 2m. to I4h. 6m. Transit of Jupiter's Sat. III. 

 5. 9h. Saturn in opposition to the sun. 

 15. Venus. Illuminated portion of disc = o"936, of Mars- 



= o '900 . 

 17. loh. 34m. Minimum of Algol (/!) Persei). 

 22. loh. 59m. Moon in conjunction with a Virginis- 



(Spica). 

 24. Saturn. Outer minor axis of outer ring = l8""o8. 

 28. 9h. 51m. to llh. 6m. Moon occults 21 Sagittarii 



(mag. 4-9). 



28. ilh. Jupiter in conjunction with moon. Jupitet 



3° 37"' S. 



29. oh. Saturn in conjunction with moon. Saturn 



3° 34' S. 

 29. 8h. 33rn. to gh. 4Sm. Moon occults d Sagittarii 

 (mag. 4-9). 



Black Si-ot on Jui'Iter.— On June 2, Sig. J. Comas Sola, 

 working at the observatory of Barcelona with a six-inch Grubb- 

 equatorial (power 200), noticed a strange marking on System II. 

 ot the planet's belts. From the lime at which it passed the 

 central meridian on that day its longitude would appear to be 

 about A = 73°i ; its latitude would be about 15°. 



The tone of the spot is almost black, with a light garnet 

 tinge, and might without close attention be mistaken for the 

 shadow of a satellite. It is very sharp and circular, but or> 

 careful examination a very pale penumbra is seen before and 

 behind the spot itself, the posterior penumbra being the more 

 prominent of the two. 



No signs of this spot were apparent on May 31. 



Ten-year Greenwich Star Catalogue for 1890. — 

 The second ten-year star catalogue recently issued from the 

 Royal Observatory forms Appendix II. to the Greenwich 

 Observations for 1S9S, and contains the reduced places of 6892 

 stars for the epoch iSgo'o, from observations made with the 

 transit circle during the period 1887-1896. 



The various corrections investigated are described at length, 

 one interesting point brought out being that the observations 

 from 1895-1S99 show a diurnal change in the position of the 

 nadir, the observations taken about noon and midnight giving 

 positive corrections to the observations made near the time of 

 sunset. 



Comparisons are also given with the data of other standard 

 catalogues, from some of which the proper motions of 174 stars 

 are deduced. 



New NebuL-E. — In the Couples rendus (vol. cxxxii. pp. 

 1465-1467) M. Bigourdan gives a descriptive table of twenty- 

 one new nebulce discovered with the north-west equatorial of the 

 Paris Observatory, bringing up the number found in this way 

 to 392. 



Parallax of m Cassiopei.^e. — The eighteenth volume of 

 " Contributions from the Observatory of Columbia University " 

 contains an investigation of the parallax of n Cassiopeia, made 

 by Mr. G. N. Baur from the Rutherfiird photographic measures 

 of twenty-eight plates of the region taken during 1870-1873. 



The final value determined for the parallax is 

 7r = o"'238±0'OI4. 



A table is also included showing the positions of fifty-six of 

 the neighbouring stars used in the determination. 



NEGATIVE AFTER-IMAGES AND COLOUR- 

 VISION. 

 T7OUR years ago I described an apparatus by which apparent 

 -'■ transformations of colour could be produced (Proc. Roy. 

 Soc, vol. Ixi. p. 268; Nature, vol. Ivi, p. 12S). The essen- 

 tial part of it is a disc, partly black and partly white, having an 

 open sector at the junction of the black and white portions, as 

 shown in Fig. I. If such a disc is caused to turn five or six 

 times in a second while its surface is strongly illuminated, a 

 coloured object placed behind it and viewed intermittently 

 through the opening generally appears to assume an entirely 

 ditferent hue, more or less approximately complementary to the 

 true colour of the object. A piece of red ribbon, for example, 

 is seen as bluish-green and a green one as pink. The eflfectis 

 due to the formation of negative after-images upon the white 

 portion of the di.sc. 



