EXTINCT STARS. PHYSICAL HISTORY OF EARTH. 57 



our sun itself will be, some seventeen millions of years 

 hence. 



The connection of Astronomy with the history of 

 our planet has been a subject of speculation and research 

 during a great part of the half- century of our existence. 

 Sir Charles Lyell devoted some of the opening chapters 

 of his great work to the subject. Haughton has brought 

 his very original powers to bear on the subject of 

 secular changes in climate, and CrolTs contributions to 

 the same subject are of great interest. Last, but not 

 least, I must not omit to make mention of the series of 

 massive memoirs (I am happy to say not yet nearly 

 terminated) by George Darwin on tidal friction, and the 

 influence of tidal action on the evolution of the solar 

 system. 



I may perhaps just mention, as regards telescopes, 

 that the largest reflector in 1830 was Sir W. Herschel's 

 of 4 ft., the largest at present being Lord Rosse's of 6 

 ft. ; as regards refractors the largest then had a diameter 

 of 11^ in., while your fellow-townsman Cooke carried 

 the size to 25 in., and Mr. Grubb, of Dublin, has just 

 successfully completed one of 27 in. for the Observatory 

 of Vienna. It is remarkable that the two largest tele- 

 scopes in the world should both be Irish. 



The general result of astronomical researches has 

 been thus eloquently summed up by Proctor : ' The 

 sidereal system is altogether more complicated and 

 more varied in structure than has hitherto been sup- 

 posed ; in the same region of the stellar depths co-exist 

 stars of many orders of real magnitude ; all orders of 

 nebulae, gaseous or stellar, planetary, ring-formed, 

 elliptical, and spiral, exist within the limits of the 



