240 Mr. H. F. Xewall [Feb. 9, 



extending over nearly 80° of solar latitude from the eastern equatorial 

 region towards the sun's north pole, the exposure being such that 

 only the inner parts of the corona are shown. The photograph gives 

 a quite inadequate representation of what one sees visually of the 

 corona. The exposure was made so that this inner coronal light 

 might be made to give the greatest photographic contrast in the fine 

 details ; in order to get that, the exposure must be short, and the 

 result is that the fainter outlying parts of the corona do not appear at 

 all. If we take a longer exposure, as was done in the next photo- 

 graph which I now show, we lose the details of the inner part and 

 gain some more of the outer part, but still the impression conveyed is 

 that of a bright corona close to the moon, the black body of the moon 

 just hiding from us the sun and a very small amount of the inner- 

 most corona close to the sun. A nearer approach to what is seen 

 visually is given by the picture which I now show, viz. a small-scale 

 photograph that the Astronomer Royal's party were able to get at 

 Sfax ; it shows, first of all, the anxiety that the party must have had 

 about clouds, for on it are portrayed the clouds seen in the neighbour- 

 hood of the sun ; but it also gives one a much better idea of the 

 sort of gradual way in which the rays of the corona stretch out and 

 become gradually invisible as they pass outward. One sees the 

 delicate radiance stretching out in all directions. I was able at 

 (xuelma to trace a particular ray visually ; it was easy to estimate the 

 extent to which the ray stretched out towards Mercury, for that planet 

 was visible. My estimate of the extension gave between five and six 

 diameters of the moon, that is, about three degrees ; whereas the 

 photographs only show an extension of 90 minutes, a degree and a 

 half ; but the precautions which would have been necessary to take a 

 photograph of such delicate extensions of streamers were such as 

 would be wanted in photographing the delicate details of cirrus cloud, 

 hence it is not surprising that the photograph shows less than the eye 

 could trace. 



Then I have to show you some fine large-scale photographs taken 

 by the Astronomer Royal at Sfax. This one shows the bank of pro- 

 minences and a great lot of detail in the lower region of the corona. 

 This next one shows detail further away from the edge of the moon. 

 The next slide shows still greater detail, particularly these great 

 streamers coming away in the direction of Mercury, and also showing 

 a (lark rift or streak which was noticed in the corona on the east side. 



Then we have a series of superb pictures on a very much larger 

 scale, showing great detail in the lower corona. One sees the gradual 

 eclipse of the great bank of prominences as the dark body of the 

 moon moves in front of it in successive exposures. You observe those 

 details in the corona — how some of these bright curved lines arch 

 over the northernmost i)eak of the prominences. Then here we see 

 some of these intersecting arches over other prominences. And then 

 if we pass on to the western side of the moon's hmb, we find other 



