NA TURE 



January 13, 1910] 



node of its orbit, wliilst the earth will pass the same point 

 eighteen hours later. For an encounter between the tail 

 and the earth to take place, it is shown to be necessary 

 that the latter should be 22,100,000 km. {13,812,500 miles) 

 Jong, and that its breadth should be such that it extends, 

 from its axis earthwards, 400,000 km. (250,000 miles). 



The accompanying chart shows approximately the 

 apparent path of the comet, according to Mr. Crommelin's 

 ephemeris, up to .\pril 5. 



was re-observed at its returns in 1857, 1S70, 1877, i8qo, 

 and i8g7, but it escaped observation, being unfavourably 

 placed, in 1903. 



Mr. Lynn, who gives these particulars in No. 41S of the 

 Observatory, also recalls some of the historic occurrences 

 which have coincided with the returns of Halley's comet. 



Oppositions of Mars, and Si.multaneous Disappear- 

 ances OF Jititfr's Satft.i.ttes, 1800-1999. — Two useful 



Apparent Path of Halley's Comet, ijio, January s-April 5. 



The Total Solar Eclipse of May 8. — From the Times 

 of January 5 we learn that Australian observers are 

 already , well advanced in their preparations for the 

 observation of the total eclipse of the sun, in Tasmania, on 

 May 8. The conditions of the eclipse — the sun's altitude 

 will be only about 8° — are not sufficiently favourable for 

 the sending of a Government expedition from this country, 

 but the Australian Eclipse Committee is being assisted, by 

 the loan of instruments, &c., by the Joint Eclipse Com- 

 mittee of the Royal, and Royal Astronomical, Societies. 



The observations will probably be made from the 

 locality of Port Davey, fourteen hours' journey from 

 Hobart, in difficult country, and a reconnaissance of the 

 district is being arranged for by the Surveyor-General of 

 Tasmania. Messrs. Baracchi, Baldwin, and Merfield are 

 to form the expedition from the Melbourne Observatory, 

 and contingents are expected from the Perth, Sydney, and 

 Adelaide institutions. 



Mr. Frank McClean, of Tunbridge Wells, who was so 

 successful at the 1908 eclipse on Flint Island, is about to 

 start for Tasmania, privately, equipped with instruments 

 for photographing the corona and the chromospheric 

 spectrum, &-c. 



Comets due to Return this Year. — In addition to 

 Halley's, two other comets are due to pass through peri- 

 helion this year. The first is known as Tempel's second 

 periodical comet, discovered in 1S73 July 3 at Milan. Its 

 period is about 55 years, and it was re-observed in 1S78, 

 1894, 1899, and 1904, making its perihelion passage, on 

 the last occasion, in November; it should therefore return 

 this coming spring. D'Arrest's comet, discovered in 1851, 

 is the second object, and is due to return during the 

 summer of this year. Its period is about 6i years, and it 

 NO. 2098, VOL. 82] 



long-date ephemerides are given by M. Enzo Mora in No. 

 4379 of the Astroiiomisclw Nachrichten. The first gives all 

 the dates of the oppositions of Mars between the years 

 1800 and 1999, the dates of, and the distances and apparent 

 diameters at, perigee, and the relative maximum brilliancy 

 of the planet at each opposition. In the second table are 

 given full particulars of the thirty-six occasions, during 

 the nineteenth and twentieth centuries, on which the four 

 Galilean satellites of Jupiter were, or will be, simul- 

 taneously invisible ; the next occasion is not until October 

 21, 1913. 



A Brilliant Fireball. — In No. 418 of the Observatory 

 Mr. Denning describes the path of a brilliant fireball which 

 was observed at Harrow and at Bournemouth on November 

 7, 1909. The true path of this meteor was over Tours 

 and Angers, in France, at a height of from fifty-nine to 

 forty-five miles, and, on the assumption that its radiant 

 was near e Tauri, at 58°, -1-9°, the motion was due east 

 to west. Observations from France, where the meteor 

 must have appeared very bright, are desirable. 



Ancient Ideas of the Physical World. — -In an article 

 which appears in No. 72 of La Revue des Idies (December 

 15, 1909), M. Leon Jaloustre gives an account of the 

 ideas held by the ancients, at different epochs, anent the 

 physical constitution of the universe. Most of these ideas 

 were, of coiu'.se, connected with astronomy, and the hypo- 

 theses of philosophers from Plato onwards are discussed 

 in a very interesting manner. 



Minor Planets. — In Astronomische Nachrichten, No. 

 4380, Dr. Neugebauer continues the list giving the adopted 

 numbers and the orbital elements of minor planets. The 

 present table includes Nos. (661) to (673) inclusive, which 

 were discovered in 1908. 



