1912] on the Total Edipao of the Sun, April 1011. P.f.l 



individuallv studied msu(tll 1/ 'duj day when the sun shines, and in l.SDl 

 a means was afforded of photographin// in a few minutes, on one plate, 

 all the prominences situated on the sun's limb. 



The solution of these and other problems which might be men- 

 tioned are gradually reducing the importance of observing eclipses, 

 and it is well within the bounds of possibility that in the near future 

 all the main solar enquiries will be able to be conducted without 

 waiting for their occurrence. 



In recent years, among the most important' work of eclipse ex- 

 peditions, that of the study of the form and chemistry of the chro- 

 mosphere and corona has taken first place, the chromosphere being that 

 ring of rosy light from which the prominences project. 



Even now the research on the chemistry of the chromosphere is 

 in process of being divorced from eclipse work. This is due to the 

 magnificent work that is being carried on at th(! Mount Wilson Solar 

 Observatory with large-scale instruments. At that Observatory the 

 chromospheric spectrum has been photographed in full sunlight. 

 The method employed, while surpassing, in accuracy of wave-length 

 measures, those made from eclipse spectra, may in time equal or 

 even possibly exceed them in detail. 



Thus the chemistry and form of the corona are practically the 

 only large inquiries which are restricted to eclipses, and probably we 

 may not have long to wait before even these form part of the daily 

 routine of solar physics observatories situated in good observing 

 localities. 



Time will not permit me to tell you even briefly how the special 

 results obtained during eclipses help the advancement of solar and 

 celestial physics. 



When it is remembered, however, that our sun has a temperature 

 of about 7000° at its surface, and perhaps several hundreds of thou- 

 sands of degrees at its centre — that the very sunspots which appear 

 to us as black spots on his surface are brighter than the brightest 

 arc lamp — then the importance of the study of every attainable part 

 of this very effective group of furnaces in and out of eclipse is 

 imperative for the advancement of knowledge. 



If one be permitted to refer briefly to the progress of our know- 

 ledge of the form, origin, and chemistry of the corona, you are well 

 aware that its shape is not the same at every eclipse, but that there 

 seems to be a systematic change going on, extending over several 

 years (Fig. 1). A study of these forms has shown that the changes 

 repeat themselves about every eleven years, and since the mean daily 

 areas of sunspots are known to have a periodicity of this length of 

 time, their close association is generally conceded. It happens, how- 

 ever, that when the coronal streamers are most prominent in highest 

 solar latitudes, and when at the same epochs the mean daily spotted 

 area is at a maximum, the mean latitudt; of the spotted area is very 

 low and only about 15°. Thus there seems reason to question the 



