18S9.] President's Address. lix 



place of each star being correct to within about 5". You are all 

 aware that the great international scheme for securing a photographic 

 chart of the whole sky down to the 14th magnitude has been 

 successfully floated and that the Cape will have a share in the work ; 

 our observatory and dome are up at the present time and work will be 

 commenced in a few months. With the new telescopes, exposures of a 

 few minutes will be sufficient to secure stars to the 14th magni- 

 tude, and exceptional precautions are taken to secure accuracy. 



I will only mention one other result of recent photography, viz., in 

 connection with long exposures. A good many years ago Prof. 

 Tempel announced that he could see a faint large nebula extending to 

 a considerable distance from the star Merope in the Pleiades ; such an 

 announcement naturally caused the most lively interest, but the 

 evidence in favour of its visibility was most conflicting ; some of the 

 best observers with large instruments were utterly unable to detect 

 anything of it, and again it was seen and sketched similarly to Prof. 

 Tempel's description by others. The balance of probability, however, 

 I think, was in favour of its non-existence. A few years ago Mr. 

 Isaac Roberts, a Liverpool merchant who has devoted his spare time 

 to astronomy, took up the subject of astronomical photography with 

 the best instrumental adjuncts that money could supply. He has 

 devoted his attention chiefly to the results of long exposures and has 

 reaped truly astonishing success. With an exposure of from three to 

 four hours he finds that not only is the Merope nebula a reality, but 

 that the whole region of the Pleiades isj swarming with nebulous matter 

 which is quite invisible to the naked eye ; the photographic plate 

 recording the accumulated energy of these faint masses of light which 

 are quite unable to affect the retina of the eye. 



Mr. Roberts has since shown some wonderful results from long 

 exposure and there is no doubt but that there is a rich harvest 

 to be gathered in this direction. 



AT THE OBSERVATORY. 



The new Heliometer at the Observatory has been at work now 

 for about a year and a half : it has been employed chiefly by Dr. 

 Grill for the determination of stellar parallaxes. With it he has 

 accumulated material for the determination of the parallax of a dozen 

 -«tars varying from the 1st to the 4th magnitude, and a similar work 

 has been carried out at Yale College Observatory for the Northern 



