102 . Mr. David Gill [May 23, 



My object now is to generalise, to put out the conclusions that 

 must be drawn from these two tables of parallax (Tables I. and II.), 

 and to see what are the broad lessons that they teach us. 



A glance is sufficient to show that neither apparent magnitude 

 nor apparent proper motion can afford a definite criterion of the 

 distance of any fixed star — that different stars really differ greatly in 

 absolute brightness and in absolute motion. 



And now what is the work before us in the future ? 



The great cosmical problem that we have to solve is not so much 

 what is the parallax of this or that particular star, but we have to 

 solve the much broader questions — 



1. What are the average parallaxes of stars of the first, second, 

 third, and fourth magnitudes, compared with those of fainter 

 magnitude ? 



2. What connection does there subsist between the parallax of a 

 star and the amount and direction of its proper motion, or can it be 

 proved that there is no such relation or connection ? 



With any approximate answer to these questions we should pro- 

 bably be able to determine the law of absorption of star-light in space, 

 and be provided with the data at present wanting for determining 

 with more precision the constant of precession and the amount and 

 direction of the solar motion in space. And who can predict what 

 hitherto unknown cosmical laws might reveal themselves in the course 

 of such an investigation ? 



It is important to consider whether such a scheme of research is 

 one that can be realised in the immediate future, or one that can 

 only be carried to completion by the accumulated labours of succes- 

 sive astronomers. 



I have very carefully considered this question from a practical 

 point of view, and I have prepared a scheme, founded on the results 

 of my past experience. I have submitted that scheme for the opinion 

 of the most competent judges, and in their opinion, as well as my 

 own, the work can be done, with honest hard work for one hemi- 

 sphere, within ten years. I have offered to do that work for the 

 southern hemisphere with my own hands, and a proposal for the 

 necessary instruments and appliances is now under the consideration 

 of my Lords Commissioners of the Admiralty. I need hardly add 

 that in this matter I look confidently for that complete consideration 

 and that efficient support which I have never failed to receive at their 

 hands since I have had the honour to serve them. 



The like work will be undertaken for the northern hemisphere by 

 my friend Dr. Elkin, who is now in charge of the heliometer at Yale 

 College in America. It is at present the finest instrument of the 

 kind in the world, and a photograph of it you have already seen 

 upon the screen. 



I most earnestly trust that we may be granted health and 

 strength for this work, and that no unforeseen circumstances will 

 prevent its complete accomplishment. 



