PROCEEDINGS. 287 



approaching that condition, will be the most powerful telescope 

 that has ever been made. With this he purposes to take 

 photographs far finer than any which lie has yet obtained, and I 

 have not the least doubt, from what I have seen in Mr. Common's 

 Observatory and Laboratory, that before very many months are 

 over, we shall have some magnificent photos of nebulae from his 

 hands. 



" I have here also a picture of a sun-spot, taken in M. Janssen's 

 famous Observatory at Meudon in the suburbs of Paris. The 

 original photograph of the suit was 7'78in. in diameter, and it 

 was so perfect that it bore enlarging until the picture of the sun 

 of which this spot picture is a part is 1 4 feet 9 inches in diameter. 

 Here you can see portrayed all the features which the best 

 telescope in the best atmosphere reveals. There is the dark 

 central umbra, the lace-like margin, penumbra, the great flame- 

 like masses of light poised as it were over the umbra, and round 

 the whole the faculaj like a ring of light, and so perfect is the 

 relation of all, that you seem to be looking into a hole when you 

 look at this photograph of a sun-spot, just as you do when viewing 

 one with a large telescope under the most favourable conditions, 

 but you will have some measure of the difficulty of obtaining 

 such pictures when 1 tell you that it stands alone, M. Janssen or 

 any other astronomer lias no second. Most of those who have 

 tried hard to get such pictures say that the air must have been 

 marvellously still and pure when it was taken. The actual 

 diameter of the large spot was 19,300 miles, and the length of 

 the whole group of spots was 53,000 miles. 



" There is yet another feature shewn here, and it is one which 

 few observers have seen as well, even with the best telescope, so 

 much does the motion of the atmosphere tend to blur the finer 

 details of the sun's surface. I refer to the so-called rice grains 

 — little indistinct points of light more or less isolated by some 

 darker matter, and yet giving a general appearance like a mass 

 of boiled rice, in which the form of the grains could still be made 

 out although much softened. It is very instructive to look closely 

 at the picture ; every here and there you come upon a darker 

 place that looks exactly like the beginning of a spot, as if the 

 rice grains were separating and so revealing a darker mass (the 

 umbra) below, and at the outskirts of the spots, there can be no 

 doubt that this is actually what is going on. These rice grains 

 are floating clouds of light, incandescent masses, floating over the 

 relative darkness, and easily separated by a great uprush of 

 hydrogen or other matter from below. But here again to get a 

 clear idea of the conditions, we must remember the actual size of 

 these rice grains, and they measure from 300 to 450 miles in 

 diameter, the majority being about 400 miles. M. Janssen, though 



