20 



NA TURE 



[July i, 1909 



Comet igoga (Borrelly-Daniel). — Several observations 

 of this comet are recorded, and an ephemeris for it is 

 given, in No. 4333 of tlie Astronomische Naclnichten. 

 Neither photographs nor eye observations show any re- 

 marlcable features, whilst the ephemeris indicates that the 

 brightness is declining ; on July 16 the comet will be but 

 .about one-third as bright as when discovered. The 

 distance from the earth is, at present, about 109 astro- 

 nomical units, and is rapidly increasing. 



The Shape of the Planet Mercury. — Referring to a 

 recent statement by Mr. Levander, that the equatorial 

 diameter of Mercury has been shown to exceed the polar 

 diameter, M. R. Jonckheere, in No. 4333 of the Astro- 

 nomische Nachrichteii, expresses the belief that the opposite 

 is the case. His observations, made during the most 

 recent transit of Mercury, indicated that the vertical 

 diameter was the greater, the values being, vertical = 9-46", 

 equatorial = 8-73" ; this is supported by other observers, 

 whose results he gives. At present the positions of the 

 equatorial and polar diameters of the planet are not 

 known, but M. Jonckheere contends that the statement 

 that the greater diameter is the one parallel to the celestial 

 •equator is, in the face of the evidence to the contrary, 

 inadmissible. 



Observations of Sun-spots, 1908. — The results of the 

 first year's regular observations of sun-spots at the Royal 

 Observatory at Capodimonte (Naples) are given by Signor 

 E. Guerrieri in No. 6, vol. iii., of the Rivista di Astro- 

 nomia (Turin). The sun was observed on 304 days, and 

 on five days was seen to be free from spots, whilst the 

 mean daily frequency of spot groups for the year was 53. 

 The first half of the year showed an excess of groups in 

 the ratio 3/2, but the analogous ratio for single spots 

 was 4/5 ; altogether, 1606 groups and 9262 individual 

 spots were observed during the year. The observations 

 are tabulated and discussed in several different ways, and, 

 if continued regularly, will form a useful supplement to 

 the work so ably performed by the other Italian observers. 



Observations of Saturn and its Rings. — In No. 4331 

 of the Astronomische Nachrichten, M. Schaer records the 

 observations of Saturn and its ring system made at the 

 Geneva Observatory, with the 40 cm. Cassegrain reflector 

 constructed by himself, during the period September 18, 

 1908, to January 24, 1909. The chief feature recorded is 

 the discovery of the new dark ring announced on October 

 7, 1908. This ring was seen, but thought to be the 

 shadow of the bright rings, on previous occasions, but 

 on October 5 it was seen to extend to the right and left, 

 and was therefore judged to be something more than 

 shadow ; on October 6 the dark ring was seen to be 

 separated, and the planet, with its usual colour, was seen 

 through the interstice, which was about 3" to 4" long 

 and 0-5" to i" broad. In January of the present vear 

 the new ring was seen more easily than during the pre- 

 ceding months. 



M. Schacr's observations also suggest the presence of a 

 cloudy, absorbing atmosphere, and the occurrence of 

 slight changes in the white ring between the crape-ring 

 and the Cassini division. The invisibility of the rings 

 when their plane passes through the earth is probably due 

 to the masking effect of the newlv discovered outer dark 

 Ting. 



Tables for the Reduction of " Standard Co- 

 ordinates " to Right Ascension and Declination. — In 

 No. 4329 of the Astronomische Nachrichten Herr A. 

 Hnatek published a series of tables for the computation 

 of a and 5 from the standard coordinates given in the 

 catalogues of the international carte dii del. A few copies 

 of these tables, printed on stout paper, have been prepared, 

 and may be obtained from the publishers for one mark per 

 copy. 



The Transv.ul Observatory, Johannesburg. — From 



the Observatory (No. 410, p. 262, June) we learn that 



from July i next the institution directed by Mr. R. T. A. 



Tnnes is to be known as the Transvaal Observatory, 



NO. 2070, VOL. 81] 



Johannesburg, South Africa. The instrumental equipment 

 is to be increased by the addition of a large refractor for 

 visual work, and a photographic astronomical telescope, 

 the gift of Mr. Franklin Adams, so that this institution 

 will now ranlc as an astronomical, as well as meteor- 

 ological, observatory. 



The Comets of 1907 and 190S. — In a brochure pub- 

 lished by Prof. Kobold, comet observers will find a very 

 useful summary of the cometary phenomena of 1907 and 

 1908. Observations of fifteen comets were made during 

 those two years, and for each object Prof. Kobold gives 

 a short summary of the observed phenomena, a set of 

 elements where available, and a table of references to the 

 publications in which the observations were severally 

 recorded. 



THE ROYAL SOCIETY CONVERSAZIONE. 



'TPHE ladies' conversazione at the Royal Society is always 

 a brilliant function, and last week the presence o'f 

 delegates and other distinguished foreign guests from the 

 Darwin celebration at Cambridge added to its interest. 

 The conversazione was held on June 24 in the rooms of 

 the society at Burlington House, and the guests were 

 received by Sir .Archibald Geikic, K.C.B., president. 

 Many of the exhibits were also shown at the conversazione 

 held in May, and were described in Nature of May 20 

 (vol. l.xxx., p. 347). Summaries of the other exhibits are 

 given below, based upon the descriptions in the official 

 catalogue, related subjects being here grouped together 

 for convenience of reference. 



Dr. If. N. Sliaui, F.R.S. : Representation of tempera- 

 tures and pressures in the atmosphere up to a height of 

 fifteen miles, on July 27 and 29, 1908. — A. Fowler: 

 Photographs of the spectrum of scandium. The photo- 

 graphs show the varying intensities of the scandium lines 

 in the arc flame, normal arc, and the arc in hydrogen. 

 Corresponding differences are found in the spectra of sun- 

 spots and prominences. — Messrs. Zeiss: Liquid crystals 

 observed under high temperatures with polarised light by 

 micro-projeciion apparatus. — Dr. F. Edridge-Greeyi : 

 Spectroscope for estimating colour perception. In the 

 focus of the instrument are two movable shutters, either 

 of which is capable of moving across the spectrum. By 

 means of the two shutters any given portion of the spec- 

 trum can be isolated. Each shutter is controlled by a 

 drum graduated in wave-lengths, so that the position ot 

 the edges of the shutters can be known. — C. E. S. Phillips : 

 Permanently luminous watch dial and military night com- 

 pass. The watch dial is transparent (glass), and the 

 figures are painted upon its upper surface. The dial is 

 backed with a compound containing a minute quantity 

 of RaBr, fradium bromide), which renders it luminous, so 

 that the time may be easily read in the darl-;. The compass 

 is arranged upon the same principle. By means of a 

 luminous disc and strip, direction may be determined at 

 night. 



If. .If. Mordey : The effect of electrostatic condensers in 

 preventing or extinguishing arcs. A suitable condenser 

 placed in shunt to an arc, or in shunt to a resistance in 

 scries with an arc, will instantly extinguish the arc. If 

 connected in shunt to the contacts before they are separated 

 it will prevent the formation of an arc even in a circuit 

 having considerable electromotive force. — The Linolite 

 Company: Metallic filament "tubolite." The metal fila- 

 ment is held at each end by a zig-zag spring to take up 

 the expansion, and is supported by anchors at two inter- 

 mediate points. The lamp may be placed in any position, 

 and can be run on an alternating current or direct current 

 circuit. — Hon. C. .I. Parsons, F.R.S. : (i) Model of leak- 

 age path device for regulating voltage of alternators. 

 The apparatus depends on the following very simple fact, 

 that while an alternating current cannot directly produce 

 a unidirectional field, it can have a strong action in 

 diminishing magnetic flux. When applied to an alternator, 

 the field magnets of the exciter are provided with a leakage 

 path, around which windings carrying alternating current 

 are placed. (2) Some samples of the blades used in steam 



