402 3Ir. David Gill [May 29, 



WEEKLY EVENING MEETING, 

 Friday, May 29, 1891. 



William Hug gins," Esq. D.C.L. LL.D. F.R.S. Vice-President, 



in the Chair. 



David Gill, Esq. LL.D. F.R.S. Her Majesty's Astronomer at the 



Cape of Good Hope. 



An Astronomer s Worh in a Modern Observatory. 



The work of Astronomical Observatories has been divided into two 

 classes, viz. Astrometry and Astrophysics. The first of these relates 

 to Astronomy of precision, that is to the determination of the posi- 

 tions of celestial objects ; the second relates to the study of their 

 physical features and chemical constitution. 



Some years ago the aims and objects of these two classes of 

 observatories might have been considered perfectly distinct, and, in 

 fact, were so considered. But I hope to show that in more recent 

 years their objects and their processes have become so interlaced 

 that they cannot with advantage be divided, and a fully equipped 

 modern observatory must be understood to include the work both of 

 Astrometry and Astrophysics. 



In any such observatory the principal and the fundamental instru- 

 ment is the transit circle. It is upon the position in the heavens of 

 celestial objects, as determined with this instrument or with kindred 

 instruments, that the whole fair superstructure of exact astronomy 

 rests; that is to say, all that we find of information and prediction in 

 our nautical ahnanacs, all that we know of the past and can predict 

 of the future motions of the celestial bodies. 



Here is a very small and imperfect model, but it will serve to 

 render intelligible the photograph of the actual instrument which 

 will be subsequently projected on the screen. [Here the lecturer de- 

 scribed the adjustments and mode of using a transit circle.] 



We are now in a position to understand photographs of the instru- 

 ment itself. But first of all as to the house in which it dwells. 

 Here, now on the screen, is the outside of the main building of the 

 Eoyal Observatory, Cape of Good Hope. I select it simply because 

 being the observatory which it is my privilege to direct, it is the one 

 of which I can most easily procure a series of photographs. It was 

 built during the years 1824-28, and like all the observatories built 

 about that time, and like too many built since, it is a very fair type 

 of most of the things which an observatory should not be. It is, as 

 you see, an admirably solid and substantial structure, innocent of any 

 architectural charm, and so far as it affords an excellent dwelling- 

 place, good library a';commodation, and good rooms for computers, no 



