SECTION II. SCIENCE 

 ASTRONOMY l 



The Sun. There were considerable total eclipses of the sun on May 8, 1910 (visible 

 in Tasmania), on April 28, 1911 (visible in the South Pacific), and on October 10, 1912 

 (visible in Brazil) : but on all three occasions bad weather rendered the expeditions for 

 observation almost fruitless. On the other hand an eclipse on April 17, 1912 (which 

 barely reached totality in Portugal, and was annular in France, Germany and Russia), 

 was favoured with particularly fine weather and produced results which open up new 

 possibilities for the utilisation of eclipses, whether total or only nearly so. A. Fowler at 

 South Kensington (magnitude of eclipse 0.92 only) observed a multitude of lines in the 

 spectrum of the reversing layer for over half-an-hour; showing that large partial eclipses 

 are available for important work of this kind. H. F. Newall at Cambridge obtained 

 photographs of 30 or 40 lines within five minutes of the greatest phase (0.90), using a 

 powerful spectrograph: he concludes that " exceedingly valuable work could be carried 

 out with an instrument of high power by an observer who, at a total eclipse, stationed 

 himself definitely outside the belt of totality, so as to obtain a large partial eclipse (say 

 0.99). At such a station his programme could be much more leisurely and complete 

 than on the central line." 



A recent outcome oj earlier eclipse work is the discussion of the polarization of the 

 corona, as observed by expeditions from the Lick Observatory. Precision has thereby 

 been given to previously vague knowledge, the maximum of 37 per cent of polarization 

 being put at 5 minutes from the sun's limb. This result accords well with the view that 

 the corona consists largely of finely divided matter ejected from the sun. 



Our knowledge of the physical and chemical constitution of the sun has however been 

 extended in recent years far more by observations made without an eclipse at all, partic- 

 ularly by work with the spectroheliograph (E. B. xxv, 618) an instrument for photo- 

 graphing the sun in light of one wave length only. With the high dispersion obtainable 

 with modern instruments, it is possible to limit the light used not merely to a particular 

 "line" but to a special part of it. In the case of calcium for instance the dark K line 

 of the solar spectrum is very wide, and over many parts of the disc it is doubly reversed, 

 that is to say, a bright line is superposed centrally on the wider dark one, while the 

 bright line has in turn a narrow dark one down the middle. This central dark line is 

 denoted by K3; its bright wings by K2, and the outer dark wings by Ki. The letters 

 v and r are often added to the suffixes to distinguish the violet wing from the red. It is 

 provisionally assumed that Ki, K2, K3 correspond to low, mean, and high levels in the 

 calcium envelope, with successively lowered pressure and temperature. Spectrohelio- 

 graphs of only moderate dispersion give pictures of K2 and K3 together: but recent 

 advances have been made by separating the components, so that for instance the K3 

 photographs taken by H. Deslandres at Meudon have revealed interesting features of 

 which only the most prominent are represented in the K2-3 pictures. At the high (K3) 

 level the sunspots disappear, the bright flocculi are less extended, and linear dark mark- 

 ings filaments as Deslandres calls them are pronounced. These filaments are even 

 better shown when the light selected for use is the central part of the red line of hydro- 

 gen. Besides the filaments, Deslandres has described a network of fine streaks which 

 he calls alignments, most of which are faintly dark, and a few feebly bright. One view 

 of their nature is that they are the higher and cooler parts of prominences seen projected 

 on the sun's disc, and appearing dark because of their absorption: in support of which 

 is cited the fact that where the filaments reach the limb of the sun a prominence is al- 

 most invariably present. According to J. Evershed, however, many large prominences 

 do not show absorption markings when the sun's rotation brings them onto the disc. 

 Against this again may be set the conclusions of A. Ricco, who has ingeniously projected 

 the prominences observed at the sun's limb onto his disc seven days later and finds a 



1 See E. B., articles enumerated in Index Volume, p. 888. 



