6 



SCIENCE. 



[N. S. Vol. II. No. 27. 



comet makes a close approach to Jupiter 

 (about 18,000,000 of miles). The orbits of 

 Brorsen's and Denning's comets appear 

 to intersect. Brorsen's comet passed the 

 intersecting point February 7, 1881, and 

 Denning's comet reached that point March 

 14, 1881. Perturbations may bring about 

 a collision. 



(6) On April 3, 1894, the second comet 

 was found by Gale, of New South Wales. 

 He used a telescope with object glass only 

 3 inches in diameter. The comet had a 

 tail 4° in length. Prof. Barnard has stud- 

 ied this comet with unusual care and taken 

 some exquisite photographs which reveal 

 many details deserving most carefal inves- 

 tigation.* 



Twenty lines were seen ia the comet's 

 spectrum. The orbit seems to be a para- 

 bola. 



(c) By the aid of an ephemeris prepared 

 by Schulhof, this second return of Tempel's 

 comet, first seen in 1873 and observed in 

 1878, was found by Finlay at the Cape of 

 Good Hope on May 8. The error in the as- 

 signed place was only 9 seconds of time in 

 right ascension and 30 seconds of arc in 

 declination. This discovery is a ' recovery ' 

 of a comet after sixteen years. 



The comet has a period of 5.2 j^ears and 

 is one of the fifteen periodic comets of which 

 at least one return has been observed. 



(d) Encke's comet belongs in the same 

 class with the preceding comet and is one of 

 the most interesting objects to the astrono- 

 mers. It was originally discovered by Pons, 

 of Marseilles, November 26, 1818. Profes- 

 sor Encke worked out its orbit and found 

 it to be 3J years, or 1208 days, the shortest 

 period of any known comet. It showed a 

 continued acceleration in its motion to 1868, 

 80 that the time of each revolution about 

 the sun was shortened by about 2^ hours. 

 After 1868 the acceleration appeared to be 

 diminished by one-half. 



*See Astronomy and Asiroj)h!jsics for June, 1894. 



The cause of this pecuUar acceleration 

 was first thought to be due to a ' resisting 

 medium ' in space or near the sun, but that 

 theoiy is now abandoned and the idea is 

 gaining ground that there is some unde- 

 tected perturbation due to planetary attrac- 

 tions. 



The thirt3'-third return of thjs comet was 

 discovered independentlj' by three observ- 

 ers, Perrotin at Nice, Wolf at Heidelberg 

 and CeruUi at Teramo, on October 31 and 

 November 1. All these astronomers were 

 aided by the ephemeris calculated by Back- 

 lund. 



(e) E. Swift, son of Lewis Swift, formerly 

 of the Rochester observatory but now lo- 

 cated in California at the Lowe Observatory, 

 discovered on November 21st the last comet 

 of the year 1894. There seem to be good 

 reasons for believing this comet to be the 

 ' lost or mislaid ' comet found by De Vico 

 at Rome, August 22, 1844. It was expected 

 to return in 1850, but ' failed then and sub- 

 sequently to keep its appointment.' 



SOLAR PARALLAX. 



Dr. Arthur Anwers published Volume 

 V. on the German Seliometer Observations 

 of the Transits of Venus, 187^ and 1882. In 

 this volume the discussion of the obser- 

 vations is given. The final value of the 

 Solar Parallax from the two transits is 

 8."896±0."0216. This corresponds to a dis- 

 tance of 91,000 000 miles. This value difiers 

 considerably from the value 8. "81 obtained 

 by Harkness in 1891.* 



This planet was in better position for ob- 

 servation during the opposition of 1894 than 

 that of 1892, although the planet was 

 farther from the earth. Observei-s have 

 noted that the south polar spot completely 

 disappeared ; that during the gibbous phase 

 there were irregularities seen at the termin- 



*Solar Farallax and Us Belated Constatits. 



