402 



KNOWLEDGE. 



Octob!;k. 1911. 



1805. 1819 were all winter returns, at all of which the comet 

 was independently discovered, its periodicity not being detected 

 till after the 1819 return. 



Five revolutions of Jupiter are equal to 21662-94 days. 



.M.ARS. — The season for this planet is again coming on. 



Phobos. Node 43 •42. 49°-70: Inclination 37--75. 36°-42: 

 Perimars 251" -0. 213°- 6 : ecc> 0-0205. 0-0068. 



It is interesting to compare these results w-ith those deduced 

 by Dr. Hermann Struve in 1898. He showed that under the 

 joint influence of the equatorial protuberance of Mars and solar 

 perturbation the pole of each orbit plane would describe a 



1786— Jan. 30-88 



1 795— Dc 



M-45 



IiUtrrval. 



21739''-' 



21740"-(i 



1805— Nov. 21-51 



1819— Jan. 27-26 

 1822— Mav 23-97 

 1825— Sept. 16- 28 

 1829— Jan. 9-75 

 1832— Mav 3-99 

 1835— .-Vug. 26-37 

 1838- Dec. 19-02 

 1842— Apr. 12-03 



9 



21729" 

 2 1725'' -3 

 2 1722'' -4 

 21719"-2 

 21716"-() 

 21712''-4 

 2 1708'' -8 

 2 1705'' -4 



Perihelion 



1845— .-^ug. 9-()l 

 1848 — Nov. 26-09 

 1852— Mar. 

 1855— Jul V 

 1858- Oct. 

 1862- Feb. 

 1865— May 

 1868— Sept. 

 1871— Dec. 

 1875- Apr. 

 1878— J ulv 

 1881— No\. 

 1885— Mar. 

 1888— June 

 1891— Oct. 

 1 895— Feb. 

 1898— Mav 



14-71 



1-04 

 18-37 



6-25 

 27-93 

 14-62 

 28-81 

 1 2 - 99 

 26-17 

 15-30 



7 ■ 6 + 

 28- (JO 

 17-99 



4-75 

 26-8(1 



Inter\al. 



2 1704'' -3 

 2 1704'' -8 

 2 1705'' -5 

 1 2 1 706'' - 



1901— Sept. 15-47 



Tahlk a. 



53T 



The opposition of November, though at a greater distance 



than the two last, is favourable on account of the planet's 



north declination. Work has already begun ; Professor 



Lowell notes that successful photographs of the canals were 



taken in August, and that the two canals near Syrtis Major, 



announced as new at the last apparition, have again been seen. 



M. Jarry Desloges notes Mare Cinnnerimn and Lacus Solis 



as pale, while Trivium 



Charontis. Mare Sirenuni. Right .Ascension 



Titanum Sinus are dark. 



He sees many canals. 



broad and pale, but easy 



to distinguish, in spite 



of the planet's distance. 



Bathys appears as in 1909. 



but quite different from 



its 1907 aspect. The 



South Polar Cap is very 



small. and apparently often 



veiled by cloud or mist. 



■■ Lowell Bulletin 50 " 

 contains a determination 

 of the relative brightness 

 of Mars' satellites. On 

 1909, September 16th, 

 both were seen with aper- 

 ture reduced to six inches, 

 and it was estimated that 

 as regards ease of seeing. 

 Phobos was intermediate 

 between Tethys and En- 

 celadus. When at the 

 same distance from the 

 limb, Phobos was con- 

 sidered to be one and 

 a-half magnitudes brighter 

 than Deimos ; the ratio 

 of diameters is deduced 

 as two and a-half to 

 fifteen to one 



circle about a fi.xed point which, in the case 

 of Phobos, is sensibly the same as Mars' 

 North Pole, but in the case of Deimos is 

 about 1° distant from it in the direction of the 

 North Pole of IMars' orbit. The radii of the 

 circles described by the poles of Deimos and 

 Phobos are respectively li|° and 1", and the 

 amount of annual movement about 6-7 and 

 162'. The perimars of each orbit advances 

 at a rate sensibly equal to the retrogression 

 of its pole. The R.A. of the pole of each 

 orbit is Node —90", and its North Polar 

 distance is equal to inclination of orbit. 

 In the diagram P, Pj . . . Pt, D, D-j . . , Dt indicate the 

 apparent positions of the poles of the orbits at the epochs 

 1877-7, 1879-8, 1892-6, 1894-7. 1896-9, 1907-5 all reduced 

 to the eiiuino.x of the last date. H, .i are the fixed points of 

 the two orbits, according to Struve, ll', A' those revised by the 

 1907 obser%ation. It will be seen that the alteration is small. 

 The new positions should not be taken as definitive, since 



theorv indicates that H' i' 



37" 



3«- 



l-"iGii-:i; 2. 



Diagrams shciwing the positions of the poles of the orliits 

 of Phobos and Deimos and of the planet Mars. 



one, of volumes and masses 

 There was some evidence of variable bright- 

 ness on the two sides of Mars, as in the case of Japetus. 

 A Washington paper has lately appeared containing a 

 determination of the orbits of these satellites in 1907, by 

 Professor H. L. Rice. The epoch is 1907. July 0-0, G.M.t!. 

 and the elements are referred to the earth's ecjuator. In each 

 element the first value belongs to Deimos, the second to 



should be parallel to 

 II A. II is only 0°-01 

 Irom the North Pole of 

 Mars' equator, which is 

 on the line A it pro- 

 duced. The diagram also 

 shows N, the North Pole 

 of Mars deduced by Pro- 

 fessor Lowell from his 

 own observations of the 

 Polar caps combined with 

 those of S c h i a p a r e 1 1 i , 

 Lohse and CeruUi, and 

 adopted in the Physical 

 I-'phemeris in the Nautical 

 .Almanac. N'. the position 

 recently given by Lowell 

 from his own observa- 

 tions alone, is also shown. 

 The agreement of N with 

 II is good in R.A., but 

 there is a puzzling differ- 

 ence of 2" in N,P.D. 



I think that ultimately 

 the Satellite method will 

 pre\ail, for their appar- 

 ent orbits are nmch larger 

 than the disc of Mars, and 

 stellar points can be more 

 accurately located than a 

 large patch of irregular shape like the Polar cap. The fact 

 that the accuracy increases with the apparent size of orbit is 

 vividly shown by the much wider departures of the points 

 marked P from the Phobos circle than of those marked D 

 from the Deimos one. The pole of Deimos' orbit, will have 

 been observed for a complete revolution about 1931, and 

 after that the deduced position of the pole of Mars will 

 probably have nearly reached finality. 



