CHAPTER XVII 



THE NAKED-EYE VISIBILITY OF 

 JUPITER'S SATELLITES 



THOUGH I have myself never succeeded in seeing any 

 of Jupiter's satellites without optical aid, I do not 

 forget that Mr. C. T. Whitmell once remarked upon 

 there being evidence, " which cannot well be set 

 aside, that the satellites are occasionally visible with 

 the naked eye." Before me are details of an observa- 

 tion made by the late Mr. H. C. Levander and two of 

 his pupils. They were supplied to Mr. Whitmell by 

 Mr. Levander 's brother. On April 21st, 1859, at 

 Devizes, shortly after 8 p.m. (and about twenty 

 minutes before the appearance of a splendid aurora), 

 they saw two of the satellites distinctly, but as the 

 sky became darker and the planet brighter, the 

 satellites gradually disappeared. They then verified 

 the observation by means of a telescope, and found 

 that they had seen III and IV, which were to the 

 right of the planet, IV being the more distant. 

 Satellites I and II were in transit at the time. Mr. 

 Whitmell's remarks upon the observation are valuable : 

 " Opposition had occurred on December 8th, 1858, so 

 that on the given date Jupiter was at a considerable 

 distance from the earth. The declination of the 

 planet was 22 degrees 50 minutes N., the altitude 



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