1906.] on Eclipse Problems and Observations. 289 



remember the photographs which he got in collaboration with Sir 

 Norman Lockyer, in India in 1898, will be able to realise the sort of 

 material which has been lost by the unkindness of the weather. 



Sir Norman Lockyer was prevented by cloud from making 

 observations at Palma at the beginning and at the end of totality ; 

 but he succeeded in getting some valuable photographs towards the 

 middle of totality. With a powerful prismatic camera the green ring 

 was photographed, showing the distribution in the corona of that 

 unknown element which gives rise to the bright green line in the 

 spectrum of the corona. I am sorry that I am not able to show you 

 an illustration of this, because the result has not yet been published. 

 Other pictures were successfully obtained showing the form of the 

 corona. 



I am fortunate in being able to show you slides which have been 

 lent me through the kindness of the Astronomer Royal ; and if I 

 show you a large number of the records which our party obtained at 

 Guelma, I hope that I may be excused for seeming to dwell unduly 

 upon them, but I naturally know more about them than about the 

 results got by other observers. 



One cannot have better illustrations of the difference between the 

 coronas at the " sun-spot minimum " and at sun-spot maximum than 

 those afforded by the two slides which I now show. This first one 

 was taken at Sumatra in 1901, at the time of sun-spot minimum ; 

 observe these extensions to the right and to the left in the equatorial 

 regions ; at the top these plumes stick out marking the position of 

 the north pole ; the southern region is equally well marked by these 

 plumes below. The second picture was taken at Guelma in 1905 at 

 sun-spot maximum, and shows equality of distribution of coronal 

 extension all round the limb of the sun. Here and there some of 

 the rays project further than others, but there is no sign of polar 

 plumes to indicate where the poles of the sun should be on this 

 picture. 



There is a peculiar point in connection with the appearance of 

 coronas of the minimum type. There is, so far as I am aware, no 

 difference in the form of the corona (such as one might connect with 

 perspective foreshortening) whether it is seen when the earth is in 

 the plane of the equator, say in December and June, or whether it is 

 seen when the earth is above or below that plane, say in March and 

 September. The effects of foreshortening of an equatorially extended 

 corona would be appreciably different in the two cases. But, as I 

 have said, I beheve no such difference can be found. We are, there- 

 fore, driven to imagine that the corona is not so much of the shape 

 of a great millstone, as it were, full of incandescent fog, but is rather 

 of the nature of a sort of cart-wheel with spokes radiating in the 

 equatorial plane from the sun. 



Here is a picture, obtained by Dr. Wallace at Ouelma, which 

 shows the inner part of the corona with a huge bank of prominences 



