672 



Heport — 1900. 



esting point to consider tbe relation of the size and separation of these dots tliat 

 form the image, and the rods and cones of the reckoner which determines the 

 power of the e3'e. 



Many years ago I tried to determine this question. 1 first took a photograph 

 of the moon with a telescope of very short focus (as near as I could get it to the 

 focus of the eye itself, which is about half an inch). The resulting photograph 

 measured one two-hundredth of an inch in diameter, and when examined again 

 with a microscope showed a fair amount of detail, in fact, very much as we see 

 the moon with the naked eye ; making a picture of the moon by hand on such 

 a scale that each separate dot of which it was made corresponded with each 

 separate sensitive point of the retina employed when viewing the moon without 

 optical aid, I found, on looking at this picture at the proper distance, that it looked 

 exactly like a real moon. In this case the distance of the dots was constant, mak- 

 ing them larger or smaller forming the light or shade of the picture. 



I did not complete these experiments, but as far as I went I thought that there 

 was good reason to believe that we could in this way increase the defining power 

 of the eye. It is a subject well worthy of further consideration. 



I know that in this imperfect and necessarily brief address I have been obliged 

 to omit the names of many workers, but I cannot conclude without alluding to the 

 part that this Association has played iu fostering and aiding Astronomy. A glance 

 through the list of money grants shows that the help has been most liberal. In my 

 youth I recollect the great value that was put on the British Association Catalogue 

 of Stars ; we know the help that was given in its early days to the Kew Observa- 

 tory ; and the Reports of the Association show the great interest that has always 

 been taken in our work. The formation of a separate Department of Astronomy is, 

 I hope, a pledge that this interest will be continued, to the advantage of our 

 science. 



List of Large Telescopes in existence in 1900. 



