352 



NA TURE 



[February 1 1, 1892 



chlorobromide, CClsBr, is a clear liquid which crystallizes when 

 cooled to —21°. The compound CCljBra is a solid at the 

 ordinary temperature, crystallizing in fine needles ; it melts, 

 however, to a clear liquid at 22°, and distils without decomposi- 

 tion at 135°. The density of the liquid at 25° is 2-42. It is 

 endowed with an odour recalling that of chloroform, and, like 

 the latter liquid, volatilizes rapidly at ordinary temperatures, its 

 vapour tension at 16° being equal to 21 millimetres of mercury. 

 The third chlorobromide, CClBrj, is readily soluble in ether, from 

 which it crystallizes upon cooling in the form of transparent tabu- 

 lar crystals of specific gravity 271 at 15°, and which fuse at 55°. 

 When distilled it suffers a slight amount of decomposition, a 

 little bromine vapour being liberated. Its odour very much 

 resembles that of carbon tetrabromide. It is very soluble in 

 chloroform and carbon tetrachloride, but is much more 

 difficultly soluble in alcohol. 



The additions to the Zoological Society's Gardens during the 

 past week include a Green M.onVey {Cercopithcctis calliirichus $ ) 

 from West Africa, presented by Mr. W. E. Tandy ; a Black- 

 eared Marmoset {Hapale penicillata) from South-East Brazil, 

 presented by Mr. Harley M. Usill ; two Herring Gulls {Larus 

 argentalus), British, presented by Mr. T. A. Cotton, F.Z.S. ; 

 a Dwarf Chameleon {Chamccleon ptimilus) from South Africa, 

 presented by Captain J. C. Robinson ; a Tabuan Parrakeet 

 {Pyrrhulopsis tabuan) from the Fiji Islands, received in 

 exchange ; six Dingos ( Canis dingo), born in the Gardens. 



OUR ASTRONOMICAL COLUMN. 



Report of the U.S. Naval Observatory.— The Annual 

 Report of the Superintendent of the U. S. Naval Observatory for 

 the year ending June 30, 1891, has just been received. Prof. 

 Hall has been using the 26-inch equatorial for observations of 

 double stars, and his results will soon be reduced and published 

 in a catalogue. The transit circle has been .employed by Prof. 

 Eastman in observations of the sun, moon, and planets, and 

 stars necessary for clock and instrument corrections. Prof. 

 Frisby has charge of the 9 •6-inch equatorial, and has made a 

 number of observations of comets, asteroids, occultations of 

 stars by the moan, and the transit of Mercury which occurred 

 on May 9, the first and second contacts being successfully ob- 

 served. The photogrp.phs of the transit of Venus in December 

 1882 have been reduced and discussed, but the whole of the 

 work in connection with the determination of the solar parallax 

 is not yet completed. The solar eclipse of April 15, 1893, 

 occurs under very favourable conditions, and Captain McNair 

 hopes that every advantage will be taken of this circumstance. 

 We note that on two nights a week the 9 ^^ inch equatorial is 

 set apart for the accommodation of visitors. During the period 

 covered by this Report 2360 persons availed themselves of this 

 privilege. 



Observations of Nebula and Star-Clusters. — In 

 1884, M. Bigourdan began to make micrometric measures of 

 nebulae observable at Paris, and a portion of his work, contain- 

 ing positions of nebulae and star-clusters between I5h. and i6h. 

 of right ascension, has recently been published. As an intro- 

 duction, a brief account is given of the growth of the idea that 

 nebulae represent an important stage in the development of 

 celestial species ; and it is pointed out that measures such as 

 those made at Paris will enable any proper motion to be deter- 

 mined. If successive careful measures should fail to show any 

 proper motion, numerous observations of the motion of nebulas 

 in the line of sight will furnish data for the determination of 

 the minimum distance of these bodies from the earth. M. 

 Bigourdan next traces the gradual increase in the number of 

 nebulae recorded, going backto the "Almagest,"in which Ptolemy 

 mentions six. Precise observations are said to commence with 

 Messier, and it is estimated that the co-ordinates of about 1500 

 nebulae are now accurately known. At Paris the positions of 

 nebulae have been determined relatively to certain comparison- 

 stars by the method usually adopted for comets ; the difference 

 neb.--^ being found in right ascension by the difference in the 

 times of transit, and in declination by micrometric measures. 

 The instrument employed in the work has an aperture of 0-32 



NO. 1163, VOL. 45] 



metres, and a focal length of 5*20 metres. The tabulated 

 observations are made up of eighteen columns. First the 

 N.G.C. number is given, and then the name of the discoverer 

 and the date of observation. After this, the magnitude of the 

 nebula is indicated, A nebula, just visible with the instrument 

 employed, is assigned the magnitude I3'5, this number repre- 

 senting the faintest star that it can grasp. The majority of 

 nebulae observed have magnitudes comprised between 13 "2 and 

 I3'5. The state of the sky at the time of observation has, of 

 course, been recorded, and another number is tabulated to in- 

 dicate the relative ease with which the nebula could be measured. 

 This brief outline of the Catalogue is a sufficient testimony of 

 the care with which M. Bigourdan has done his work, so far as 

 it goes. It is to be hoped that the publication of the completed 

 Catalogue is not very far ahead. 



Solar Observations.— Prof, Tacchini, in Comptes rendus 

 for January 25, gives the following resume of solar observations 

 made at the Royal Observatory of the Roman College during 

 the last quarter of 1891 : — 



Relative frequency Relative magnitude No. of 



, — ^groups 



of days ner 



of spots, without of spots, of faculae. 

 spots. 

 Q-OO 54-69 ... 8577 



o-oo 61-38 ... 5 1 '50 

 o-oo 42-18 ... 35-36 



Number of 



1891. days of 



observation 



October ... 26 . 



November... 22 . 



December... 18 



day. 



4-96 

 3 "41 

 2-68 



15-54 

 12-50 

 8-57 



A comparison of these numbers with those for the preceding 

 quarter shows a slight diminution in the phenomena of spots 

 and faculae. It should, however, be remarked that on no day 

 has the sun been free from spots, and the frequency of groups 

 remains about the same. 



The observations of solar prominences are summed up as 

 follows : — 



Number of 

 1891. days of 



observation. 



Mean 

 number. 



Mean Mean 



height. extension. 



October 

 November ... 

 December ... 



982 

 573 

 6-48 



43*6 

 35-4 

 40-2 



17 

 1-6 



2-2 ■ 



Prominences were frequently observed in September and also 

 in October, but since this month the number has slightly dimin- 

 ished. The mean number for the quarter covered by this 

 resumS'i^ about the same as that of last quarter, 



M, Marchand gives the results of solar observations made at 

 Lyon Observatory during the latter half of 1891, in the current 

 Comptes rendus. The proportion of spotted surface, expressed 

 in millionths of the sun's visible hemisphere, and the surface 

 covered by faculae expressed in thousandths of the visible hemi- 

 sphere, is stated as follows : — 



Spots. Faculae.' Spots. Faculae. 



July ... 1696 ... 382 October ... Ii8n ... 49-6 



August .. 957 ... 40-5 I November... 748 ... 39*2 

 September... 2469 ... 51-3 December ... 947 ... 50-0 



The total spotted surface is thus 7999 millionths of the visible 

 hemisphere, this being covered by loi groups. The preceding 

 half year's observations gave 65 groups and a surface of 3517 

 millionths. Spots have been more numerous in the northern 

 than in the southern hemisphere in the ratio 69 : 32. This 

 predominance of activity in the northern hemisphere also holds 

 good for faculae. The total surface covered by groups of faculae 

 is 268-8 thousandths of the visible hemisphere, as against 1363 

 thousandths in the first six months of last year. The number of 

 groups of facuire giving these values was 152 (July to December) 

 and 131 (January to June). 



Measures of the Nebula near Merope. — Astronomische 

 Nachrichten, No. 3074, contains an account of some measures 

 of the faint nebula discovered by Mr. Barnard close to the 

 bright star Merope, in the Pleiades. The measures were made 

 by Mr. S. W. Burnham with the 36 inch equatorial. The 

 position-angle and distance found by Mr. Burnham are, 

 i66°'3 and 36"-io (1891-71). These values agree very well with 

 the values i65°-8 and 36"85 (1890-92) deduced from Mr. 

 Barnard's observations of the differences of R.A. and Decl. 

 between the star and the nebula. This extremely close associa- 

 tion of a faint nebula with a bright star is most remarkable; and 

 it will be interesting to determine, by careful measures in the 

 future, whether the patch of nebulosity is drifting through space 

 with Merope and the other members of the Pleiades group. 



