PROGRESS OF MODERN ASTRONOMY 



pigeon-hole, Leverrier's calculation was coming on, his 

 tentative results meeting full encouragement from 

 Arago and other French savants. At last the labori- 

 ous calculations proved satisfactory, and, confident of 

 the result, Leverrier sent to the Berlin observatory, 

 requesting that search be made for the disturber of 

 Uranus in a particular spot of the heavens. Dr. Galle 

 received the request September 23, 1846. That very 

 night he turned his telescope to the indicated region, 

 and there, within a single degree of the suggested spot, 

 he saw a seeming star, invisible to the unaided eye, 

 which proved to be the long-sought planet, henceforth 

 to be known as Neptune. To the average mind, which 

 finds something altogether mystifying about abstract 

 mathematics, this was a feat savoring of the miraculous. 

 Stimulated by this success, Leverrier calculated an 

 orbit for an interior planet from perturbations of Mer- 

 cury, but though prematurely christened Vulcan, this 

 hypothetical nursling of the sun still haunts the realm 

 of the undiscovered, along with certain equally hypo- 

 thetical trans-Neptunian planets whose existence has 

 been suggested by " residual perturbations" of Uranus, 

 and by the movements of comets. No other veritable 

 additions of the sun's planetary family have been made 

 in our century, beyond the finding of seven small moons, 

 which chiefly attest the advance in telescopic powers. 

 Of these, the tiny attendants of our Martian neighbor, 

 discovered by Professor Hall with the great Washing- 

 ton refractor, are of greatest interest, because of their 

 small size and extremely rapid flight. One of them is 

 poised only six thousand miles from Mars, and whirls 

 about him almost four times as fast as he revolves, 



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