Report on the total solar eclipse of 1911, April 28. (Observed the expedition of the joint permanent eclipse committee to Vavau, Tonga Islands, South Pacific.)

Abstract

1. General Arrangements . The expedition to observe the total solar eclipse of 1911, April 28, was organised by the Joint Permanent Eclipse Committee, the expenses being defrayed by the Government Grant Fund. Of the few islands in the South Pacific crossed by the track of the moon’s shadow during totality, Vavau, one of the northernmost group of the Tonga or Friendly Islands, was the most suitable for observing the eclipse, the duration of totality being computed at 217 seconds, and there being a reasonable prospect of good weather. The programme of observations consisted of photographs of the corona on a large and relatively small scale for coronal detail and extension of the streamers, and photographs of the spectrum of the corona and of the lower chromosphere. For these purposes the expedition was furnished with a 4-inch photographic lens of 20 feet focal length, kindly lent by the Council of the Royal Irish Academy, and the 4-inch Dallmeyer “Abney” lens of 34 inches focal length. For the spectrum of the corona Prof. Newall kindly lent the quartz spectroscope of four prisms, presented to the Cambridge Observatory by Major Hills, in order further to investigate the ultra-violet spectrum. The fourth instrument was made up of a large 7-inch prism of 40° in combination with a 6-inch Dallmeyer portrait lens of 30 inches focal length, This objective prismatic camera gave a short but very bright spectrum, 4⋅5 cm. from H α to H ζ . The intention was to investigate the red end of the coronal spectrum on dyed plates, and incidentally to photograph the flash spectrum. The members of the expedition were Father Cortie and Mr. W. McKeon, from the Stonyhurst College Observatory, and Father E. Pigot, Director of the Observatory of St. Ignatius’ College, Rivervievv, Sydney, N. S. W., who also acted as agent for the expedition in Sydney, in the preparation of huts to cover the instruments, and in the gathering of materials for building the piers for the foundations. The Admiralty gave instructions that H. M. S. “Encounter” should convey the observers and the instruments from Sydney to Vavau and back, and that every assistance should be rendered to the expedition in the erection of the instruments and in the observations. The expedition is greatly indebted to Captain Colomb, and to the officers and men of the “Encounter,” for their enthusiastic co-operation in the work of the expedition.