158 Mr. David Gill [June 3, 



WEEKLY EVENING MEETING, 



Friday, June 3, 1887. 



Edward Woods, Esq. Pres. Inst. C.E. Manager and Vice-President, 



in the Chair. 



David Gill, LL.D. F.R.S. 



HER majesty's ASTRONOMER AT THE CAPE OF GOOD HOPE. 



The Aijplications of Photography in Astronomy. 



Little more than a year ago Mr. Ainslie Common delivered a lecture 

 in this place on the subject of " Photography as an aid to Astronomy." 

 Given by one who is a consummate master of the art of celestial 

 photography, that lecture (complete as to history and full of siigi^es- 

 tion as it was) would, under ordinary circumstances, have precluded 

 further reference to the subject in these Friday evening lectures for 

 some years to come. 



But the past year has witnessed such developments of the subject, 

 and the importance of photography in astronomy has been so much 

 advanced by the conclusions of the recent Astro-jDhotograj^hic Congress, 

 as to afford a reasonable apology for the present lecture. 



On the 16th of April last there was held at Paris a Congress 

 attended by upwards of fifty astronomers and physicists, representing 

 nearly every civilised nation in the world. It was convened for the 

 purpose of considering a scheme of international co-operation in the 

 work of charting the sky on a large scale. Or, rather, its object was 

 to obtain a series of pictures, which, taken within a comparatively 

 limited period of time, and with the necessary precautions, would 

 enable astronomers of the present day to hand down to future genera- 

 tions a complete record of the positions and magnitudes of all the 

 stars in the heavens to a given order of magnitude. The labours of 

 that Conference are now concluded, certain important resolutions have 

 been adopted, and the way has been so far cleared for giving these 

 resolutions practical effect. 



It seems of importance therefore to lay before the members of the 

 Royal Institution some account of the history of this remarkable 

 Congress, to illustrate and explain the grounds of the conclusions 

 which it has arrived at, and otherwise to bring the history of photo- 

 graphic astronomy up to the present date. I pass over the already well 

 told early history of celestial photography, except in so far as it relates 

 to star charting. It was Warren de la Kue who first called attention 

 to the means furnished by photography for charting groups of stars. 

 In his Report to the British Association at Manchester in 1861 on 

 the progress of celestial photography, he indicates a photographic 



i 



