72 SPECIAL RESULTS IN THE TJKANOLOGICAL 



the earliest view expressed by Francis Bacon, in the second 

 book of the Novum Organum. He speaks of the time re- 

 quired by a ray of light to traverse the immensity of space, 

 and throws out the question whether the stars still exist 

 which we now see sparkle. ( 136 ) One is astonished at find- 

 ing so happy a conjecture in a work whose celebrated author 

 was so far below some of his cotemporaries in mathematical, 

 astronomical, and physical knowledge. The velocity of the 

 reflected solar light was measured by Homer (November 

 1675) by comparison of the times of occultation of Jupiter's 

 satellites ; and the velocity of the direct light of the fixed 

 stars by Bradley' s great discovery of the aberration of light 

 (made in the autumn of 1727), that demonstration to our 

 senses of the earth' s movement of translation in its orbit ; 

 viz. of the truth of the Copernican system. In very recent 

 times a third method of measurement has been proposed by 

 Arago, by the phenomena of the light of a variable star ; for 

 example, Algol in Perseus. ( 137 ) We have to add to these 

 astronomical methods a terrestrial measurement, which has 

 very recently been executed with great ingenuity and suc- 

 cess by M. Fizeau, in the neighbourhood of Paris. It recals 

 to recollection an attempt of Galileo's with two lanterns, 

 which did not lead to any result. 



Erom Eomer's first observations of Jupiter's satellites, 

 Horrebow and Du Hamel estimated the time occupied in 

 the passage of light from the sun to the earth, at their 

 mean distance apart, at 14' 7"; Cassini, at 14' 10"; New- 

 ton ( 138 ), which is very striking, much nearer to the truth, 

 at 7' 30". Delambre,( 139 ) by taking into account, among 

 the observations of his time, only those of the first satellite, 

 found 8' 13"*2. Encke has very justly remarked how 



