130 A CENTURY'S PROGRESS IN ASTRONOMY. 



In 1835 Halley's comet returned to perihelion, 

 and was attentively studied by the most famous 

 astronomers of the age. It was particularly 

 studied by Sir John Herschel and by Bessel, 

 who assisted in developing Gibers' theory of 

 electrical repulsion. But the most brilliant 

 comet of the century was that which suddenly 

 appeared on February 28, 1843, in the vicinity 

 of the Sun. This great comet, whose centre 

 approached the Sun within 78,000 miles, rushed 

 past its perihelion at the speed of 366 miles a 

 second. The comet's tail reached the length of 

 200 millions of miles. The comet of 1843 was 

 however outshone, not in brilliance but as a 

 celestial spectacle, by the great comet discovered 

 on June 2, 1858, by Giovanni Battista Donati 

 (1826-1873) at Florence, and since known by 

 his name. It became visible to the naked eye 

 on August 19, and was telescopically observed 

 until March 4, 1859. There was abundance of 

 time, therefore, to study the comet, which was 

 exhaustively observed by G. P. Bond at Harvard. 

 His observations convinced him that the light 

 from Donati's comet was merely reflected sun- 

 shine, and this was generally accepted. Another 

 great comet appeared in 1861. Like that of 

 1843, its appearance was sudden, being observed 

 after sunset on June 30, 1861, when, says Miss 



