462 Astronomical Society. 



the entluisiasm in the cause of abstract science, which could carry 

 you successfully through the task thus voluntarily imposed on your- 

 self, you share with few. You have however the satisfaction of 

 knowing that so much labour has not been bestowed in vain ; for, 

 if there be any thing on which we can calculate with certainty, it is 

 that the work you have been mainly instrumental in completing, 

 must exercise a powerful influence on the future destinies of As- 

 tronomy. 



( The President then resumed his Address to the Members in general, 

 as follows : — ) 



Gentlemen, 



We have still another, and a very interesting part of the business 

 of this meeting to perform, in the delivery, to Colonel Beaufoy, of a 

 Medal for his valuable series of observations of eclipses of Jupiter's 

 satellites, communicated to this Society, and in part already printed 

 in the first part of the second volume of our Memoirs; in part 

 recently read at a late meeting, and completed up to the present 

 time, by the paper you have heard read to-night. 



The subject of the eclipses of Jupiter's satellites, is one of singular 

 interest in the history of Astronomy. The discovery of these bodies 

 was one of the first brilliant results of the invention of the telescope ; 

 one of the first great facts which opened the eyes of mankind to the 

 system of the universe — which taught them the comparative insig- 

 nificance of their own planet, and the superior vastness and nicer 

 mechanism of those other bodies, which had before been distin- 

 guished from the stars only by their motion, and wherein none but 

 the boldest thinkers had ventured to suspect a community of nature 

 with our own globe. This discovery gave the holding turn to the 

 opinions of mankind respecting the Copernican system : the analogy 

 presented by these little bodies (little however only, in comparison 

 with the great central body about which they revolve) performing 

 their beautiful revolutions in perfect harmony and order about it, 

 being too strong to be resisted. As if to confirm this analogy be- 

 yond dispute, Kepler lived just long enough to witness the discovery, 

 and to demonstrate* the extension of the same general law to their 

 periods which he had found to obtain among those of the primary 

 planets about the sun. The conclusion was irresistible ; and the full 

 establishment of the Copernican System must date from the disco- 

 very of the satellites of Jupiter. 



This elegant system was watched with all the curiosity and in* 

 terest the subject naturally inspired ; and the eclipses of the satel- 

 lites speedily attracted attention, and the more when it was dis- 

 cerned, as it immediately was, by Galileo himself, that they afforded 

 a ready method of determining the difference of longitudes of distant 

 places on the earth's surface by observations of the instants of their 

 disappearances and reappearances simultaneously n)ade. Thus the 

 first astronomical solution of the great problem of the longitude, — 



* According to Delanibre this extension of Kepler's law is due to Ven- 

 delinus. 



the 



