172 SECTION PHYSICS. 



question whatever that as solar radiation varies so must vary also the 

 whole atmospheric conditions of moisture and rainfall ; hence it is 

 most desirable that sun pictures should be obtained in a sufficient 

 number of places, in order that we may have a solar picture at least 

 every day, not only on a small scale for the position and area of the 

 spots, but on a large scale, so that we may study special phenomena 

 of the sun intimately on a large scale. Solar photography has this 

 advantage, that it can be pursued in a town ; the sun has so much 

 actinic power that it matters very little where we are placed so that the 

 sun shines. I am happy to say that in Austria they think of making 

 such observations. In Paris there seems to be a chance also, and I 

 trust that through the action of the Royal Society and the Astronomical 

 Society we shall get the Indian Government to take it up, and I 

 certainly do hope that in England we shall have a solar physical 

 observatory. 



The PRESIDENT : I am sure you will all join with me in offering 

 our best thanks to Mr. De La Rue for so complete an exposition in 

 most respects and so lucid in all, of this important subject of 

 astronomical photography. I say emphatically complete in most 

 respects because there is one point in which it is decidedly incomplete. 

 He has given us a very clear and fair idea of how these processes 

 were brought successfully into action, and how it has been managed 

 to bring out of them these great results of which he has given us 

 specimens, but he has by no means conveyed to the minds of his 

 audience how much these results are due to his own individual efforts 

 and contributions. I think I shall not say too much if I speak of 

 astronomical photography in this country at all events, and through 

 this country to most parts of the civilized world, as being indebted 

 more to him than to any one individual from its commencement to 

 the present time. 



[Mr. De La Rue here took the chair.] 



