QUESTIONS CONCERNING THE MINOR PLANETS. 195 



formed, we can imagine how complete is the transformation to 

 which the sorts of wool are subjected in the carding process. We 

 can thus readily understand how much more perfect is the card- 

 ing operation, as now performed by machinery, than anything 

 that was possible under hand manipulation. 



QUESTIONS CONCERNING THE MINOR PLANETS. 



By M. F. F. TISSEEAND, of the Institute of France. 



KEPLER, having found a break in the continuity of the 

 mean distances of the planets from the sun, boldly filled 

 it by supposing a new planet between Mars and Jupiter. The 

 publication of Bode's empiric law in 1772 helped confirm the ideas 

 of Kepler, and fixed the distance of the hypothetical planet at 

 2"8 times that of the earth. A new authority was given to this 

 conclusion after the discovery of Uranus by William Herschel 

 in 1781. The calculations of Lexell and Laplace showed in fact 

 that Uranus's distance might have been furnished in advance, 

 with a near approach to exactness, by Bode's law. At a confer- 

 ence. held in Gotha in 1796, Lalande and De Zach proposed to 

 search for the unknown planet, and to divide the labor among 

 twenty-four astronomers, each of whom should examine an hour 

 of the zodiac. 



On the first day of this century that is, January 1, 1801 

 Piazzi discovered at Palermo a star which he took at first for a 

 little comet and observed several times till the 11th of February 

 following, when illness stopped his work. Bode was the first to 

 recognize that the star could not be a comet, and thought that in 

 Ceres Piazzi had found the planet suspected by Kepler. When 

 Piazzi had become well again, he did not know where to look for 

 Ceres. It was to be sought for toward the end of the year, after 

 coming out from the glare of the sun, but no data were at hand for 

 determining its position except the geocentric arc of 3 which it had 

 traversed during the forty days it had been under observation. 



Here Gauss came to the rescue ; he was then twenty-four years 

 of age, and had had little or nothing to do with astronomical cal- 

 culations, having been occupied chiefly with the higher arithme- 

 tic. In less than a month he invented an admirable method for 

 calculating the elements of the elliptical orbit of Ceres and an 

 ephemeris, by means of which Olbers found the star again on the 

 first day of January, 1802. The mean distance of Ceres from the 

 sun is 2'77. It corresponds exactly with Bode's law, and fills the 

 gap, but with a very modest planet, having a diameter of only 

 about 200 miles. 



