president's address — SECTION A. 91 



Encouraged by the success of his spectro-heliograph. Professor 

 Hale'** has designed for tlie Yerkes Observatory, Chicago, an 

 improved spectro-heliograph, which will, when finished, carry 

 seventy-two sensitive plates, and automatically record on each of 

 them at any interval that may be desired complete pictures of the 

 spots, faculas, photosphere, and prominences in true relative position 

 on each plate. All that will be necessary will be to set the 

 telescope, wind up the machinery, and set it to work, the only 

 limits being, first, that it takes two minutes to get a complete 

 picture of the sun ; and, second, the number of plates put in the 

 wheel that carries them. 



Under the old system it was a good hour's work to record the 

 prominences alone ; the new apparatus will do the same work far 

 better in one minute. So far it has not been found impossible to 

 photograph the corona with this apparatus, but experiments are in 

 progress and confidently expected to succeed by which a modified 

 spectro-heliograph \vill photograph the corona, using only the ultra 

 violet light. 



One remarkable result of Professor Hale's spectro-heliograph 

 work is the abundance of faculse all over the sun from pole to 

 pole, and seen thus they are of curved forms, generally like the 

 figure 3, though spread over the whole surface they are strongest 

 within 40^ of the equator north and soutli, and the greater part of 

 them are invisible to the eye, and in Professor's Hale's opinion 

 they "are not to be confused with Janssen's reseau photo- 

 sperique." Janssen, in 1869, in a paper read before the British 

 Association meeting at Exeter, pointed out that it was possible 

 to isolate any particular line in the spectrvun by using two slits, one 

 being near the eye. 



On March 22nd, 1892, a photograph of Swift's comet was taken 

 at the Sydney Observatory, which shows eight narrow rays ex- 

 tending from the head. As these were all quite invisible with the 

 large refractor, it is probable that they were composed of blue or 

 violet light, because if of white light they would have been visible 

 through some of the larger telescopes turned to the comet, if not 

 through the Sydney refractor. 



Professor Schaerberle"^, at Lick Observatory, has recently photo- 

 graphed the corona by the method of absorption introduced by 

 Dr. Huggins, and has obtained satisfactory pictures. He con- 

 ducted the Lick Expedition to observe the solar eclipse of April 

 16th, 1893, and in his report he says that the observations and 

 photographs of the eclipse taken confirm his opinion of the 

 structure of the corona, and his photographs of it by Dr. Huggins'^ 

 method. One of the eclipse pictures shows the dark sun 4in. in 

 diameter, and the corona round it covers a plate l«in. x 22in. 



In March and April, 1893, selected parts of the Milky Way were 

 photographed at Sydney with the large star camera and specially 

 sensitive plates, with the results that parts that look nebulous in 



