xlii President'' s Address. [Axxg. 29, 



from being as concordant as could be wished. The observation 

 consists in determining the displacement (due to motion to or from 

 the earth) of a line in the star's spectrum as compared with the same 

 line given by an artificial light ; but the smallness of the displacement 

 and the unsteadiness of the stellar line caused by the earth's atmos- 

 phere almost make a satisfactory observation hopeless. Here again 

 photography promises to come to our assistance, the sensitive plate 

 does what the eye cannot do, it shews the accumulated effect of the 

 various positions of the unsteady line by a space the centre of which^ 

 corresponds to the mean position of the line. There is very little' 

 doubt that this method, w^hich was suggested and has already been 

 successfully tried by Vogel, will entirely supersede the older one of- 

 eye observations. 



On the many other applications of photography to astroQomy I 

 shall not dwell, as it is only a short time ago that we had an 

 exhaustive account of them from ])r. Gill ; but it is abundantly' 

 evident that the co-operation of electricity and photography have 

 completely revolutionised the older astronomy and opened up new 

 and extensive fields of research. 



Many new observatories have sprung into existence in the last 12 

 years, one I am glad to say in South Africa, viz., the Natal Obser- 

 vatory at Durban. The latest and greatest is the Lick Observatory 

 in California ; it is situated on Mount Hamilton at an elevation of 

 4,200 feet above the sea, it possesses the largest refracting telescope 

 in the world and an excellent climate, and wdth a staff of experienced 

 observers it has a great future before it. 



There are numbers of minor points in which substantial progress 

 has been made, but an account of them all would fill a volume. I 

 have endeavoured to lay before you the more important ones, and I 

 hope I have succeeded in giving you some idea of the problems that 

 have been solved in the last few years and of the unceasing activity 

 and earnestness of the devotees of the noblest of sciences. 



