NEWS FROM HERSCHEL' S PLANET. 137 



all his presentations, as they can study Mars, or Jupiter, 

 or Saturn. 



When we add to this circumstance the extreme 

 faintness of Uranus, we cannot wonder that Herschel 

 should have been unable to speak very confidently on 

 many points of interest. His measures of the planet's 

 globe were sufficiently satisfactory, and, combined with 

 modern researches, show that Uranus has a diameter 

 exceeding the earth's rather less than four and a half 

 times. Thus the surface of Uranus exceeds that of our 

 globe about twenty times, and his bulk is more than 

 eighty times as great as the earth's. His volume, in 

 fact, exceeds the combined volume of Mercury, Venus, 

 the Earth, and Mars, almost exactly forty times. But 

 Sir W. Herschel was unable to measure the disc of 

 Uranus in such a way as to determine whether the 

 planet is compressed in the same marked degree as 

 Jupiter and Saturn. All that he felt competent to 

 say was that the disc of the planet seemed to him to 

 be oval, whether he used his seven-feet, or his ten-feet, 

 or his twenty-feet reflector. Arago has expressed some 

 surprise that Herschel should have been content with 

 such a statement. But in reality the circumstance is 

 in no way surprising. For as a matter of fact 

 Herschel had been almost foiled by the difficulty of 

 measuring even the planet's mean diameter. The dis- 

 cordance between his earliest measures is somewhat 

 startling. His first estimate of the diameter made it 

 ten thousand miles too small (its actual value being 

 about thirty-four thousand miles); his next made it 



