Annual Address to the Members. lix 



anticipating a decision, which time alone can stamp with the seal of 

 absolute authority." 



I think that a less over-cautious judgment might have agreed to 

 accept the evidence which Henderson produced. Be that as it 

 may, a different eye and a different circle, the eye of Sir Thomas 

 Maclear and his new transit circle, did confirm Henderson's con- 

 clusion. 



Bearing in mind the traditions of the Observatory, the importance 

 for the sake of science which these investigations presented, and the 

 advantages which modern instruments and improved methods might 

 afford, I acquired possession of a heliometer which I had used in 

 Lord Crawford's (then Lord Lindsay) expedition to Mauritius. This 

 instrument had been kindly lent by its noble owner for my expedi- 

 tion to Ascension, so that I was well aware of its good qualities. A 

 young American astronomer, Dr. Elkin, who was my guest for two 

 years at the Cape, joined me in making a series of researches on the 

 distances of certain southern stars. 



We determined together the distances of nine interesting stars. 

 I shall briefly state here only that naturally one of our chief objects 

 was to confirm, or otherwise, Henderson and Maclear's results for 

 the parallax of a Centauri. It was confirmed ; a Centauri proved 

 not to be quite so near us as they had made out, but very nearly so. 

 The result was that from four independent series of observations, 

 two of them by Elkin and two by myself, the parallax of a Centauri 

 was proved to be three-quarters of a second of arc. It is therefore 

 beyond all doubt that Henderson's discovery was a real one, though 

 the result was somewhat too great. Herschel's verdict must there- 

 fore be confirmed, and the palm for first breaking down the barriers 

 that separated us from any knowledge of the distances of the fixed 

 stars be accorded to the memory of the Cape Astronomer, 

 Henderson. So far as all existing researches go, a Centauri is the 

 nearest of the fixed stars. Eegarding the faint comparison stars as 

 practically infinitely distant, let us try to realise how near or far 

 distant o Centauri really is. If we wish to deal with distance so 

 immense, we must adopt a more convenient unit of measure. The 

 most convenient unit for our purpose is the number of years that 

 light would take to reach us. Light takes almost exactly 

 500 seconds of time to come from the sun ; this is a figure easy to 

 remember, and is probably exact to a single unit. The sun is in 

 round numbers 93 millions of miles distant. The parallax of 

 a Centauri is three-quarters of a second of arc ; therefore its distance 

 is 275,000 times the distance of the earth from the sun, and there- 

 fore light, which travels to the earth from the sun in 500 seconds 



