322 THE PRESIDENT S ADDRESS. 



day should unite in undertaking a delineation of the heavens by 

 photographic means, and that the work should he carried out at 

 stations selected for the purpose, -with instruments identical in 

 all their essential parts. It is intended to adopt the fourteenth 

 magnitude as the limit, and also to take a second series of photo- 

 graphs with a shorter exposure, to include stars only to the 

 eleventh magnitude, and thus render possible the construction of 

 a general star catalogue. The extent of such a catalogue may 

 be estimated when it is understood that the total number of stars 

 to the 11£ magnitude is considered to be about 3J millions. The 

 directors of about twenty observatories have already promised to 

 co-operate, and the whole sky in both hemispheres has been 

 divided into separate portions for the convenience of the differ- 

 ent observatories. A 13-inch photographic refractor has been 

 lately mounted at the Royal Observatory, Greenwich, specially 

 constructed for these observations, and some trial photographs 

 have been already taken with it. I believe the scheme will be 

 in active operation in some places, before the close of the present 

 year. 



The feasibility of such a project has been for sometime made 

 apparent by the beautiful stellar photographs of Paul and 

 Prosper Henry, of the Paris Observatory, and of Mr. Isaac 

 Roberts, F.P.S., of Liverpool. In a photograph taken by Mr. 

 Roberts, on August 14, 1887, with an exposure of one hour, a 

 space of about two degrees square in the Milky Way, in the 

 constellation Cygnus, is represented. In this space there are 

 probably about a half-dozen stars visible to the naked eye, but 

 in the photograph no less than 16,000 are recorded, all of which 

 you will remember are separate suns, and possibly the ruling 

 centres of systems of worlds. At the Lick Observatory, Cali- 

 fornia, Mr. Barnard has also taken some very successful 

 photographs of a portion of the Milky Way, and of the nebula 

 in Andromeda. For many years he had observed an inky-black 

 hole, surrounded by nebulous matter, but in a negative of that 

 region taken on August 1, 1889, not only is this black hole 

 clearly shown, but the entire cloud-like formation about it, and 

 myriads of stars, are also faithfully depicted, not one of which 

 had ever been directly viewed by the eye of man through a 

 telescope. I understand that the exceeding beauty of a glass 



