l62 



NATURE 



[June 12, 1890 



<i)G.C. ifi"! 

 (2)6.0.4234 

 ■(3).r Serpentis 



(4) 5 Bootis ... 



(5) a Coronae 



(6) W Cygni 



Mag. 



White. 

 Bluish. 

 Reddish-yellow. 

 Yellow. 

 Bluish-white. 

 Reddish. 



R.A. 189a 



IS 12 57 

 i6 39 51 

 IS 43 48 

 IS II 6 

 15 30 o 

 21 31 53 



Ded. 1890. 



+ 5643 

 + 24 o 

 + 18 29 

 + 33 44 

 + 27 S 

 +44 S3 



Remarks. 

 (i) This is a long white nebula in Draco which was described 

 by Sir John Herschel as "a superb ray nebula." The G.C. 

 description is : '* Considerably bright ; very large ; very much 

 extended in the direction 155° ; at first very gradually, then 

 pretty suddenly brighter in the middle, where there is a nucleus." 

 In Herschel's 20-foot reflector it was seen to be 7^' long. The 

 spectrum of the nebula has not been recorded. 



(2) This is one of the planetary nebulce, and according to Dr. 

 Huggins its spectrum shows the three bright lines usually seen 

 in nebulae. He also noted that F was the faintest line, and that 

 there was a faint continuous spectrum. The spectrum was re- 

 observed by Vogel in 1872, and he observed two additional 

 lines near wave-lengths 518 and 554. It is important that these 

 lines should be confirmed, and comparisons made with the flutings 

 of carbon and manganese at 517 and 558 respectively. The 

 existence of these lines will further tend to prove the connection 

 between comets and nebulse, for two bands in these positions 

 have frequently been observed in cometary spectra. It is not 

 improbable that a third cometary band, near A. 468, may also 

 appear in the nebula, as a line near that position (A 470) has 

 been recorded by Dr. Copeland and Mr. Taylor in other nebulDe. 

 Unfortunately, a raiher large aperture is required for this obser- 

 vation ; with a lo-inch refractor I have not been able to more 

 than glimpse the additional lines seen by Vogel. The G.C. 

 description of the nebula is : "A planetary nebula ; very 

 bright; very small ; round; disk and border." It is not ad- 

 visable to employ a cylindrical lens in searching for faint lines, 

 •even though the nebula is a small one. 



(3) Vogel describes this star as a fine one of Group II., but 

 Duner states that the bands are narrow, 4 and 5 being little 

 more than lines. He also notes that the spectrum approaches 

 Class Il.a (Group III.). It is therefore probable that the spec- 

 trum is an intermediate one, and will show some of the lines 

 characteristic of Group III. Any differences in these lines, 

 either in positions or relative intensities, from those seen in stars 

 •like the sun, should be noted, as they will form valuable criteria 

 for the subdivision of the Class II. a stars of Vogel into two 

 groups — one of increasing temperatures (Group III.), and the 

 other decreasing (Group V,), 



(4 and 5) The first of these has a spectrum of the solar type, 

 and the second one of Group IV. (Gothard). The usual 

 observations are required in each case. 



(6) The range of this variable is very small — 5*8-6 '2 at 

 maximum to 67-7'3 at minimum — and it will be interesting 

 to observe if any changes in spectrum take place at maximum 

 similar to those which occur in stars of greater range with the 

 same type of spectrum. The general spectrum is a " very fine " 

 one of Group If., but so far no variations with change of magni- 

 tude have been noted. The period is given by Gore as 120-138 

 ■days, and there will be a maximum about June 21. 



The Spectrum of Comet Brooks {a 1890). — I made 

 further observations of this comet on June 6 and 7, and found 

 that it had become considerably brighter since my last observa- 

 tion (Nature, vol. xlii. p. 112). The tail was also slightly 

 extended. The principal spectroscopic change noted was a 

 diminution in the brightness of the continuous spectrum rela- 

 tively to the carbon flutings, making the latter more distinct. 

 There was no change in the positions of the bands, and as the 

 comet has now passed perihelion, it is not likely that it will go 

 through any of the higher-temperature stages. As its distance 

 from the sun increases, it should be observed for the cooler 

 stages. The first decided change, according to Mr. Lockyer's 

 investigation;;, should be the replacing of the present "hot 

 carbon" spectrum for that, of "cool carbon," the criterion for 

 which is a fluting near \ 483. This, again, should be replaced 

 by a spectrum comisting mainly of a line in the position of the 

 •chief nebula line (A 500). 



In connection with the observations of the comet, I have also 

 made observations of the spectrum of the nebula G.C. 4058 

 (see notes for June 5). I found that the spectrum of the nebula 

 NO. 1076, VOL. 42] 



was irregularly continuous, with a very decided maximum of bright- 

 ness coincident with the carbon fluting near A 517. There were 

 also other brightnesses, the positions of which are not yet deter- 

 mined. The whole spectrum is strikingly similar to that of the 

 comet, and as the two objects are not far removed from each 

 other, this is a good opportunity for observers to satisfy them- 

 selves that comets and nebulse are intimately connected. 



A. Fowler. 

 The Planet Uranus.— M. Perrotin, of Nice Observatory, 

 has made some observations of dusky bands on Uranus, similar 

 to those that are seen on Jupiter ( Vierteljahrs<chrift des Astro- 

 nomisclie Gesellschaft). The following are some values found 

 for the position-angle : — 



1889 31 May 13 



35 



I June 20 



7 „ 30 



The mean value is 24°"5, or about 10° from the plane of ihc 

 orbit of the satellites, from which it would appear that the 

 plane of the Uranian equator differs little from the trend of the 

 satellites. M. Perrotin also found that the direction of the bands, 

 according to repeated measures, coincided with the longest dia- 

 meter. The bands do not appear always to have the same aspect, 

 but vary in number and in size in different parts of the surface. 

 This unequal distribution will, it is hoped, afford a means of 

 accurately determining the time of rotation. The oblateness 

 deduced from the measures is said to be not less than ■^^. 



Mr. Tebbutt's Observatory. — We have received the 

 Report of this Observatory for the year 1889. A consider- 

 able amount of extra-meridian work has been done during the 

 year, observations having been made of some minor planets, 

 phenomena of Jupiter's satellites, and occultations of stni-; by 

 the moon. Barnard's comet (a 1889) and Davidson's comet 

 [d 1889) were observed on eight occasions, and Brooks's comet 

 \e 1889) on two occasions. The comparison observations that 

 were made have been reduced, and sent to Asironomische 

 Nachrichten. Brorsen's periodical comet was carefully searched 

 for, with the help of Dr. Lamp's ephemeris, on December 21 

 and 25, 1889, and again on January 18, 20, and 22, but without 

 success. Comparisons have been made, both of tj ArgiAs and 

 R Carinse, with the neighbouring stars, and it is noted that the 

 former star has not sensibly varied in its lustre since the an- 

 nouncement of its sudden increase of magnitude between April 

 1887 and May 1888. A satisfactory determination of a maxi- 

 mum of the latter star was made in June 1889, and its period 

 determined as 312 days. 



New Asteroid. — A minor planet of the 13th magnitude 

 was discovered by M. Charlois at Nice on May 20. This brings 

 the number up to (S). 



CORAL REEFS AND OTHER CARBONATE OF 



LIME FORMA TIONS IN MODERN SEAS. ^ 

 ''PHE vast organic accumulations known as coral reefs are, 

 undoubtedly, among the most striking phenomena of 

 tropical oceanic waters. The picturesque beauty of coral atolls 

 and barrier reefs, with their shallov/ placid lagoons, and their 

 wonderful submarine zoological and botanical gardens, fixed at 

 once the attention of the early voyagers into the seas of equa- 

 torial regions of the ocean. Questions connected with the 

 peculiar form, the structure, the origin, and the distribution of 

 these great natural productions have, from the very outset, 

 puzzled and interested all those who delight in the study of 

 natural things. In this communication we propose to point out 

 and discuss some of the more general phenomena of oceanic 

 deposits, with special reference to the functions of corals and 

 other lime- secreting organisms, and the accumulation of their 

 dead shells and skeletons on the floor of the great oceans. 



Coral reefs are developed in greatest perfection in those ocean 

 waters where the temperature is highest and the annual range is 

 least. It may be said that reefs are never met with where the 

 temperature of the surface water, at any time of the year, sinks 

 below 70° F., and where the annual range of temperature is 

 greater than 12° F. Bermuda, which is the coral island the 

 farthest removed from the equator (lat. 32° N.), and one or two 

 other outlying reefs, may be, in a sense, exceptions to this 

 ' Paper read on December 2, 1S89, before the Royal Society of Edinburgh, 

 by John Murray, LL.D., Ph.D., and Rtbert Irvine, F.C.S. 



