274 Professor Arthur Schuster [Feb. 13, 



symmetrical with respect to it. No such symmetry can be noticed 

 in the corona which ajDpears at times of maximum sunspots. The 

 streamers extend irregularly all round the body of the sun, but do 

 not reach so far as the long extension of the first type. 



With respect to the nature of the corona, there are four alterna- 

 tives. It consists of matter either (1), forming a regular atmosphere 

 round the sun ; or (2), matter projected from the sun ; (3), matter 

 falling into the sun ; or finally (4), matter circulating round the sun 

 with planetary velocity. 



The choice between these observations must be made by careful 

 analysis of the light received by us from the corona. We possess 

 w^ell-known methods to distinguish between light which is sent out 

 from bodies which are self-luminous, and light which is reflected ; 

 and we may even detect violent motions of luminous matter. 



The lecturer then explained in detail the photographs of the 

 spectrum of the corona and prominences as photographer! in the 

 West Indian eclipse. The principal results may be summarised as 

 follows : — 



(1) The greater part of the light sent out by the solar corona 

 is due to matter which is self-luminous, and probably in a solid or 

 liquid condition ; the maximum of luminous intensity is displaced 

 towards the red end of the spectrum as compared with sunlight, 

 showing that the temperature of the luminous matter is lower than 

 that of the solar surface. 



(2) A comparatively small part of the light is reflected sunlight. 

 The relative importance of reflected and independent light seems to 

 differ in different eclipses, a point which will no doubt receive careful 

 attention on future occasions. 



(3) Hydrogen and calcium, which are the main constituents of 

 solar prominences, do not form part of the normal spectrum of the 

 corona. The hydrogen lines are visible only in the parts overlying 

 strong prominences. The violet calcium lines known as H and K, 

 though visible everywhere, are stronger on that side of the corona 

 which has many prominences at its base. 



If this result is confirmed on future occasions it w^ould prove that 

 the matter of the corona is partly formed by substances thrown out 

 from the body of the sun. 



(4) The gaseous constituents of the corona, which seem rich in 

 spectroscopic lines, cannot at present be identified with any terrestrial 

 elements. 



(5) The matter of the corona does not revolve with planetary 

 velocity round the sun. 



Photometric measurements have been made during the last eclipse 

 by Professor Thorpe with instruments designed by Ciiptain Abney, 

 and one of their results allows us to compare the corona in this 

 respect with the one observed by Langley in 1878. Thorpe and 

 Abucy find the luminous intensity between eight and nine minutes of 

 arc away from the sun's limb to be about the twentieth part of the 



