570 



NATURE 



[December 29, 1921 



Next Year's Total Solar Eclipse (September 21, 1922). 

 By Major William J. S. Lockyer. 



IN September of the coming year there will be 

 a very favourable total eclipse of the sun, and 

 several expeditions are preparing- to proceed to 

 stations on the narrow track of the moon's 

 shadow. This eclipse is a member of an impor- 

 tant family, from the point of view of solar 

 physics, because one of its predecessors was the 

 memorable eclipse of August i8, 1868. On this 

 occasion the astronomical equipment was enriched 

 for the first time by the use of the spectroscope 

 for such work, and the important discovery of the 

 gaseous nature of the solar prominences during 

 that eclipse was the forerunner of very rapid 

 advances in solar research. The track of the 

 shadow was slightly to the north of the coming 

 one, and passed over North-East Africa, India, 

 Java, and North Australia. It was in India that 

 the memorable observations were made. 



Fig. I. — Shadow track during total solar eclipse of September 21, 1922 



The two immediate predecessors of the coming 

 eclipse took place on September 9, 1904, and 

 August 29, 1886. The first of these was confined 

 to the Pacific Ocean, where no observations were 

 made. The second commenced in the north of 

 South America ; the track then crossed the Atlan- 

 tic Ocean, finally crossing South Africa, and ter- 

 minating in Madagascar. Unfavourable weather 

 prevented many observations being made. 



The line of totality of next year's eclipse com- 

 mences on the north-east coast of Africa, leaving 

 it at Somaliland. It then cuts through the 

 Maldive Islands, which lie to the south-west of 

 India, skirts the East Indies, but passes over 

 Christmas Island, which is situated about 200 

 miles to the south of the sound between Sumatra 

 and Java. The line next strikes the Australian 

 continent at a region called Ninety Mile Beach, 

 crosses the continent nearly centrally, and leaves 

 it at the coast of South-East Queensland. It 

 ends in the ocean just to the north of the North 

 Island of New Zealand. 



The line of totality is shown on the accompany- 



.'SO. 2722, VOL. 108] 



ing figure, and it will be seen that it affords four 

 regions (marked with circles) well distributed 

 along it from which observations could be made. 



On the north-east coast of Africa the eclipse 

 occurs when the sun is near the horizon, so this 

 region is not favourable for observational work. 

 Farther east, the Maldive Islands present a good 

 -station. There the sun is well up, having an alti- 

 tude at eclipse time of about 34°, and the duration 

 of the total phase is 4m. los. The weather 

 prospects seem to be good. It is probable that 

 special arrangements would have to be made to 

 reach the islands, as there is no scheduled line of 

 steamers. It is not yet known which of the islands 

 will be occupied, but Admiral Sir A. Mostyn 

 Field points out (Monthly Notices, R.A.S.. 

 vol. 81, No. 5) that care must be taken as regards 

 selection owing to possible landing difficulties. 

 Thus in the case of the island 

 of Dambidu (lat. 2° 5/ N., 

 long, 'jf 34' E.) charts seem 

 to indicate a broad shelf of 

 reef more than a mile in width, 

 extending from the island on 

 the lagoon side : the presence 

 of coral heads separated bv 

 deep pools may therefore be 

 expected. It is very probable 

 that Mr. John Evershed, the 

 director of the Kodaikanal and 

 Madras Observatories, will pro- 

 ceed to this station, and his 

 work will include spectroscopic 

 observations on a large scale. 



At Christmas Island, in the 

 Indian Ocean, the sun will be well 

 up towards the zenith — in fact, it 

 nearly noon there — and the duration of 

 will be 3m. 40S. This island is not 

 in the centre of the zone of totality, 

 but about fifty miles from this centre. The 

 prospect of clear weather at this tropical island 

 is only moderate, but from experience at such 

 islands little dependence can be laid on average 

 conditions of weather. 



The British Joint Permanent Committee has 

 decided to occupy this island. Two members of 

 the staff of Greenwich Observatory. Mr. H. 

 Spencer Jones and Mr. P. J. Melotte, have been 

 chosen to proceed there to obtain the necessary 

 photographs. The special object of this expedi- 

 tion is to make a new determination of the devia- 

 tion of the light of stars in the gravitational field 

 of the sun. The instrument to be employed is 

 the 13-in. astrographic telescope on a special 

 equatorial mounting. It may be remarked here 

 that usually on such expeditions telescopes 

 mounted equatorially are not used. The tubes 

 containing the object glass and camera attach- 

 ments are generally mounted horizontally, and the 



will be 

 totality 

 exactly 



