May 13, 1909] 



NA rURE 



Spectroscopic Binauies. — A number of newly discovered 

 spectroscopic binaries are discussed briefly in No. 3, vol. 

 .\.\ix., of the Astrophysical Journal. Prof. Campbell re- 

 ports that, in the course of the regular observing pro- 

 gramme with the Mills spectrograph, the following eleven 

 stars have been shown to have variable radial velocities : — 

 y Persei, J Tauri, (*■ Tauri, I (53) Eridani, f Aurigje, 

 P Orionis, j3 Canis Majoris, v Draconis, 70 Ophiuchi, 

 III lli'rculis, and ^ Cygni. Of these, 7 Persei and 

 / liridani probably have long, whilst 6^ Tauri and 13 Canis 

 Majoris probably have short, periods, and 70 Ophiuchi 

 is a well-known double star with a period of eighty-eight 

 years. 



.As the result of the recijnt investigations of the D. O. 

 Mills expedition to Santiago, Chile, Dr. Heber D. Curtis 

 announces that five stars, f Canis Majoris, t Puppis, 

 o \'olorum, d Carinas, and 1/ Velorum, have been shown 

 to be spectroscopic binaries, the first four probably having 

 long periods. Two other stars, v Puppis and v Octantis, 

 also photographed at Santiago, are announced by Prof. 

 \\". H. Wright as spectroscopic binaries. 



Harvard College Oeseuvatory. — Prof. Pickering's re- 

 port of the work performed at the Harvard College 

 Obscrvatorv during the year ending September 30, igoS, 

 directs special attention to the large amount of publica- 

 tion during that period. With the help of a monetary 

 gfrant from Mr. Fairchild, no fewer than six volumes of 

 annals have been completed, the publications of the twelve 

 months e.Kceeding in amount those of the first thirty years 

 of the observatory's existence. Fourteen thousand settings 

 with the polarising photometer related chiefly to variables 

 of the .-\lgol type, and will serve to determine their light- 

 curves and epochs of minima. About thirteen hundred 

 settings on the asteroids Iris and Eros showed that at 

 present their light does not vary. Four thousand one 

 hundred stellar photographs were taken at Cambridge and 

 3509 at Arequipa during the year, and numerous nebula, 

 stars with pf.culiar spectra, six meteor trails, and many 

 variable stars were thus discovered. 



THE PERCY SLADEN TRUST EXPEDITION 

 TO THE INDIAN OCEAN. 



Final Explor.^tions.' 

 "T^HE field work of the above expedition has now been 

 completed with the return of Messrs. H. Scott and 

 J. C. F. Fryer from the Seychelles and ".Aldabra on 

 March 29. Mr. Scott has brought with him more than 

 40,000 insects from the .Seychelles as a result of eight 

 months' collecting. Among these are many remarkable 

 forms, including a very large number of beetles, which 

 will take some years to determine. The tropical rains of 

 December and January brought out a great variety of 

 insects not previously obtained. 



Mr. Fryer spent nearly five months in Aldabra. His 

 preliminary report, which is subjoined, is of great interest 

 as showing the foundations on which that so-called atoll is 

 built. .Aldabra contains about fifty square miles of land, 

 and was supposed to be a typical atoll, almost completely 

 land-locked. It was also known for its still containing 

 numerous gigantic land-tortoises, and for its partially 

 peculiar avifauna. Some sand from it, which I obtained 

 in 1905 in Seychelles, showed the presence of a consider- 

 able quantity of silica, on account of which we deemed 

 its exploration necessary. 



Mr. R. H. Rastall, who has examined some fragments 

 of the .Mdabra rocks, forwarded to me by post, writes 

 that " they promise to be of very great petrological interest, 

 as they consist for the most part of spherulitic and 

 devitrified volcanic glasses." • 



J. Stanley Gardiner. 



T arrived in .Mdahra at the end of the south-east mon- 

 soon. Owing to the extreme dryness of the season I 

 decided to explore the island at once with regard to its 

 geological formation, leaving its zoology and botany until 

 the wet season. 



1 For earlier reports 

 Novemlier 9, December 5 



Nature, April 13, August 10, October 5. 

 1905, January 25, 1906, and December 17, 1908. 



NO. 2063, VOL. 80] 



I had four camps, i.e. on Michel Island, at Takamaka 

 on Main Island, on Esprit Island, and on Picard Island,, 

 from which I examined every portion of the so-called 

 atoll. Owing to the dense and almost impenetrable scrub 

 there were always great ditViculties, as I had ev^ywhere 

 to cut paths ; in addition, I cleared several broad sections 

 from the sea to the lagoon in order to get a clear idea 

 of the sequence of the rocks and vegetation and of the 

 relative elevations. 



The nature of the ground and of its vegetation is such 

 that the land may be divided into four somewhat irregular 

 zones, from the lagoon outwards, as follows : — 



(i) Mangrove swamp — varying in size up to nearly a 

 mile in maximum breadth. 



(2) Champignon — the surface much metamorphosed, 

 highly crystalline, coral rock, usually with sharply defined' 

 dark portions, in which the crystals appear to be imbedded 

 in a brown amorphous substance. It has evidently been 

 subjected to heavy rain denudation, its surface being a 

 mass of points and pits. The vegetation is a scrub of 

 Peinphis acidula. 



(3) Platin — fairly smooth, composed mainly of coral frag- 

 ments and reef debris with a few shells, weathering into 

 large flat slabs with soil accumulating in the crevices. 

 In places are larger depressions, in which there are usually 

 clumps of trees. The soil is guano, with a mixture of 

 disintegrated rock. The vegetation is varied, containing 

 numerous small bushes and trees, Pandanus, Ficus, 

 Euphorbia, &-c. ; the fauna is also varied, and compara- 

 tively rich. 



(4) Shore zone — largely of blown sand, with a stunted 

 and wind-swept vegetation ; large clumps of Pandanus, 

 Tournefortia, and Scaevola everywhere very numerous. 



In a broad sectional clearing which I made at 

 Takamaka, the seaward reef commences with a fissured 

 edge, succeeded by a sand flat, the sand being bound 

 together by beds of grass-like Cymodocea, its rhizomes 

 o-reatly overgrown by Lithothamnia ; the buttresses 

 between the fissures are themselves largely covered with 

 sand ; live coral is almost absent ; not far from the edge 

 are a few small boulders of dead coral, all much encrusted 

 with Lithothamnia ; a few species of seaweed are found 

 in the pools left at low tide. The landward edge of the 

 reef is formed of cliffs 12 feet to 15 feet high, just out- 

 side which is usually a small depression in the reef with 

 2 feet or 3 feet of water. The cliffs are sloping, not 

 overhanging, and are divided into buttresses ; they consist 

 of a mass of corals cemented together with lime. The 

 corals are all in the position in which they grew, and so 

 perfect that they give the impression that they are only 

 just dead. On the landward side of the cliffs is a ridge, 

 2 feet or 3 feet higher, of grass-covered sand ; this marks 

 the seaward edge of the shore zone, which is about_ 250 

 yards wide, the sand being shallow and lying on a basis of 

 coral rock. Then comes a ridge, 4 feet to 6 feet higher, 

 the rock more solid and less denuded; this, the highest 

 part of the section, is some 25 feet above sea-level. From 

 the landward side of this ridge the level gradually de- 

 creases to about 10 feet above sea-level. It passes mto a 

 zone of Champignon, which here lies outside the Platm 

 zone, which latter extends to the mangrove swamp. The 

 Platin is all very similar in appearance, except that it is 

 more wooded near the lagoon ; it terminates with a sharp 

 drop through the last 4 feet or J feet to the lagoon surface. 

 At Takamaka there is a spring of fresh water and a grove 

 of large Calophvllum and Ficus trees. This spring, with 

 three others all 'King between Takamaka and the lagoon, 

 is the only constant source of fresh water on the islands. 

 The section finishes at Abbot's Creek, which is a narrow 

 passage from the lagoon with a thick undergrowth of 

 mangroves on each side ; its bed is rocky, and covered with 

 very" fine white mud ; at its termination in the land it 

 passes between small cliffs, all much overhung and 

 obviously breaking down. 



In another section, which passes from Vert Island in 

 the lagoon northward to the sea, the country is all, with 

 the exception of the shore zone, of the Champignon tvpe, 

 Platin being entirely absent. There is a gradual slope 

 from the lagoon, becoming steeper at the beginning of 

 the shore zone ; right up to the latter salt water is often 



