ECLIPSE OF THE SUN.

Dominion, Volume 4, Issue 1086, 27 March 1911, Page 8

ECLIPSE OF THE SUN.

SCIENTIFIC EXPEDITIONS. SOME INTERESTING PACTS. Twenty-seven thousand miles to see an eclipse, of the sun, lasting three minutes and a half. That is all. The eclipse is to take place on April 29, and the best place to see it in the whole world will be tho Tongan.lslands. To do this two British expeditions are now on their way ,to Varan, one of the islands in the Tongan 'Group, and by the time they get homo again they will have travelled the distance mentioned. The members of the two expeditions arrived in Sydney recently by the Ii.JI.S. Otway.

Oue of the expeditions is led by the Eov. father A. L. Cot-tie, with Brother M'Keon as his assistant, and the other by Br. AV. J. S. Lockyer, with Sir. F. M'Clean as assistant. Father Cortie and Brother M Keon are from Stoneyhurst College, Lancashire. The former is tho accredited observer of tho eclipso on behalf of tho Royal Society and tho Royal Astronomical Society. Dr. Lockyer, who is in charge of the other expedition, is from the fcolar Physics Observatory, South Kensington, Londoiu and his party is under tho. direction of the. Board of Education. The two expeditions will combine in their work at tho time of tho eclipse under tho command of Father Cortie. The party will also be accompanied by the Rev. Father Pig-jot, of Rivcrview College, Sydney, Mr. J. Brooks and Mr. W. E. Raymond, of Sydney. The Admiralty has placed a man-of-war—the Encounter—at their disposal, so that they will have tho expert assistance of the officers and crow in erecting the instruments. They were to leave. Sydney on March 25. An Australian expedition, under tho command of Mr. Barrachi, Government astronomer of Victoria, will sail on March 28.

The instruments that the expeditions are taking with them .are somo of the best that can bo procured. The principal apparatus is a Gin. focus lens "20ft. long, with a 4in. aperture to photograph tho details of the inner corona. This will give an imago on the photographic plate 2 1-lOin. in diameter, without magnifying, and during tho three minutes and a half that the eclime will last, from six to -sight plates will bo exposed. Each of them is Bin. by lOin. in size, so that in addition to tho sun disc the corona will also be photographed. Tho camera docs all tho work now, because it is more accurate, and gives more detail than tho human eye. Lenses 10ft. long have been used for this woi'k.at times, but the -Oft. lens is moro frequently used. Tho lons carried by the expedition has already done duty in recording the eclinses that took place in 1300 and 1003. In addition to the big lens they have a smaller 4in. lens of 33in. focal length to photograph the outer corona. Then, for tho spectrum of tho corona, there is a large quartz prism spectroscope. Thoio is a chance that all this trouble and expense might go for nothing. If April 29 is a cloudy morning at Vavau tho expedition may not be able to see the eclip.'e. This, however, is not likely. Tho Joint Permanent Eclinse Committee of th- Royal. Society and the Royal Astronomical Society studied the weather prospects fully twelve months p.ijo, and Aime to the conclusion that Vavau was going lo have good woatlm , on April 20. Of course, they were not able to forecast ihc weather to a day so far ahead, but it is a season of fine wer.ther tliero, and prospects are all in the expedition's favour.

Spaaking (n a "Sydney Morning Herald'' interviewer lost wceF of the to ba made, Father Cortio explained that it was expected that tho ecnsrnl form of thn corona this time would !?p what is called (he minimum typo that is associated with a few sun spots. There will bo lons wings or streamers in tho equatorial regions, and Ihe polar regions will be open, but filled with more or loss strong rays. These will be. thn main features, but in every eclipse thcro are special features that have '.o be photographed and studied. As soon as tho moon covers the sun tho solar corona, which can only !>"■ observed at such' times, comes out. The knowledge of tin , physics of the sun is important, and it i> only at times of total eclipso that we can get a knnwlodee of some of ths phenomena of the sun. Comparatively little is known about Hv>. corona, and it is only at times of total eclipse that it can !:<■■ studied. Terrestrial magnetism is connected with changes in the sun, and in those changes the coromi nlays a preat part. An adequate knowledge of the physics of the sun c?;inot be obtained unless sonie'.hinjr is known about fho corona, and (akiiig tho chances of bad weather there is not more, than five minutes for observing the corona in two years.

Au American expedition will prob'ablv ma'ks observations from Nas-au Island, nnd a Gorman expedition will oporato from ono of the Sunioaii Islands.