80 



KNOWLEDGE 



[April, 1902. 



the third. The story of Wriinjjol, tlio reh-brated Russian 

 traveller, (Hioted l)y Mr. G. F. Chambers from Arago, that 

 when in Siberia lie once met a hunter who said, jiointing 

 to Jupiter, "I have just seen that large star swallow a 

 small one and vomit it shortly afterwards," is a b(?autiful 

 specimen of the traveller's tale. \Vrangcl explains the 

 hunter's remark as referring to an immersion and sub- 

 sequent emersion of the third satellite. It escaped 

 Arago's notice that it takes tlie third satellite over a week 

 to pass from one elongation to aiiotlier, and that further, 

 as the satellite would have reappeared on the ojiposite side 

 of Jupiter from that on which it disa|)peared, the hnnter 

 would have scarcely described the incident as he did. 



An opera- glass of course easily shows the satellites of 

 Jupiter, and one opticiilly perfect should suffice to elongate 

 Saturn when the ring is fully open or show the phase of 

 Venus at greatest brilliancy. 



The movements of Mars are sufficiently difTerent from 

 those of the other four planets for him to be considered 

 by himself ; the chief features in his case being the length 

 of time in which he remains out of sight on the far side of 

 the sun, and the very great difference between his apparent 

 size when nearest to the earth and when farthest from it. 



The East Horizon at 2 a.m. on the morning of 1881, June 22. 



The syliodic periods of Mercury and Venus stated above 

 are 1 16 and 584 days respectively ; those of Jupiter and 

 Saturn are 34 and 13 days longer than an entire year, but 

 the synodic period of Mars is 50 days more than two 

 years. During the greater part of this time he is moving 

 eastward amongst the stars at a pace of only a little less 

 than a degree a day. As he approaches opposition his 

 pace slackens down until, like Jupiter and Saturn, he 

 becomes stationary and then recedes for a time westward. 

 This period of recession begins about six weeks before 

 opposition and lasts about six weeks after. 



The chief interest of Mars, as a subject of observation 

 without the telescope, is the opportunity which he gives, 

 especially when he is in the more distant parts of his orbit, 

 and therefore relatively fainter, to compare him as to his 

 brightness with the stars near to which he passes. This 

 is a work which needs doing, and which anyone could 

 undertake, yet it has been almost entirely neglected. 



Three other planets are just within the limits of visibility 

 under favourable circumstances, Uranus, Ceres and Vesta. 

 To these we may now possibly add a fourth, Eros. But 

 while the three above mentioned might be seen at any 



opposition, Eros, if ever l)right enough, will only be so at 

 one opposition in thirty-seven years. 



One feature of the planetary mandi will always attract 

 attention and give pleasure to the observer, even though 

 no practical result Ije drawn frum it; that is the way in 

 which from time to time two or more of them will come 

 into close proximity to each other, or it may be to some 

 bright fixed star or to the moon. Thus on September 15, 

 1186, all the five chief planets were in conjunction together 

 in the constellation Virgo to .the east of Spica. lu much 

 more recent times, four of the five chief planets came 

 together in the constellation Aries, Mercury being the 

 only missing member, and this conjunction was made the 

 more impressive by the presence in the midst of the group 

 of the waning moon. This beautiful s])ectacle was 

 witnessed in the earlv morning of June 22, 1881. 



ORIGIN OF A DISTURBED REGION OBSERVED 

 IN THE CORONA OF 1901, MAY 17-18. 



In a preliminary report* of the observations of the Sumatra 

 eclipse by the Crocker Expedition from the Lick Observa- 

 tory, I called attention to an unusual area of disturbance 

 in the corona in the north-east quadrant. At the time of 

 writing that report no observations of the Sun's surface 

 were available from which to investigate the source of this 

 disturbance. Through the courtesy of the Astronomer 

 Royal, Royal Observatory, Greenwich, we have received a 

 set of positives on glass of negatives of the Sun taken at 

 Dehra Diin, India, on May 17th, 18th, 19th, 20th, 21st, 

 22nd, 26th, and 28th, 1901. These photographs are on 

 a large scale, 7^ inches to the Sun's diameter, and furnish 

 the desired observations. They show an intimate con- 

 nection between activity on the Sun's surface as observed 

 in the sun-spots and faculse, and the corona. 



The photographs of May 17th and 18th show no spots 

 or other evidences of activity on any part of the .Sun's disc. 

 This absence of spots was noticed before the eclipse at the 

 station in Sumatra. The photograph of May 19th, 

 however, shows a medium-sized spot which has just come 

 into view around the east limb. On this date the spot is 

 little more than a line, owing to foreshortening, ^' in length 

 surrounded by faculae. On the 20th it is J' in length 

 (;>., north and south), followed' at a distance of *' by 

 several small spots forming a close group. On all sides of 

 the group, except the preceding or west side, is a large 

 area of faculse. The principal spot is cornpact, with well- 

 defined umbra and penumbra, and shows no more changes 

 from day to day than are usually observed in the same 

 period. The group of small spots following, however, 

 shows traces of greater activity, principally growth. 



Following are the co-ordinates of the principal spot 

 deduced from the plates of May 19th and 28th, the 

 longitudes being measured from the centre of the disc : — 



Greenwich 



Civil Time. Longritude. Latitude, 



h. m. s. ° 



1901 May 19 3 30 37 807 East + 90 



28 7 29 37 -M!7 West + 90 



From these positions are deduced the foUowmg co- 

 ordinates of the spot at the time of the eclipse in Padang: — 



Greenwich 

 Mean Time. Longitude. Latitude, 

 h. m. s. ° ° 



1901 May 17 17 40 37 93-8 East +9-0 



From this it will be seen that the spot was on the 

 opposite side of the Sun at the time of the eclipse and 

 within 4*-' of the limb. Following are the position angles 

 of the spot as projected on the limb, and of the apex of 



* Lick Observatory Bulletin, No. 9. 



