4 



SCIENCE. 



[N. S. Vol. XIV. No. 340. 



of an error of Wollaston, one of his contem- 

 poraries, in assigning a place to a star where 

 none existed. Piazzi found, however, an 

 eighth magnitude star not before noted, and 

 upon repeating the observation the follow- 

 ing evening, it was found to be in motion. 

 Piazzi carefully followed the planet until 

 February 11, when he fell ill, and his ac- 

 tivities were for some time suspended. 

 Meanwhile letters had been sent to Oriani, 

 at Milan, and Bode, at Berlin. About this 

 time, however, it may be remembered that 

 another individual, not wholly unknown to 

 fame, was actively employed in this part of 

 the world in the practical applications of 

 military science. We refer to one Napoleon 

 Bonaparte. This may explain the fact that 

 Oriani's letter arrived at Milan two and 

 one-half months after it was written. Gi- 

 bers, however, received that directed to him 

 at the end of two months. The planet was 

 now lost in the sun's rays and it was greatly 

 feared that it would not be recovered, for, 

 with a body so minute, unless its position 

 could be given with some approach to ac- 

 curacy the attempt to find it was an almost 

 hopeless task. This emergency brought to 

 the front the great mathematician Gauss. 

 At that time a young man unknown to 

 fame, he attacked the problem, and as a re- 

 sult produced a method for determining an 

 orbit from three observed positions which 

 completely overcame the difficulty, at the 

 same time showing its author's title to a 

 place in the front rank of mathematicians. 

 The discovery of three more planets be- 

 longing to the asteroid group soon followed, 

 Juno, Vesta and Pallas, then, after a long 

 interval came Astrsea in 1845. The dis- 

 coverer was Hencke, an amateur astrono- 

 mer, who had been watching the heavens 

 during fifteen years in the hope of this re- 

 ward. The number now known to exist is 

 near five hundred, with no indication that 

 the supply approaches exhaustion. About 

 ten years ago tb e application of photography 



to this purpose by Wolf, of Heidelbegr, 

 made possible what may be called a whole- 

 sale process. One plate, taken October 22, 

 1900, showed no less than five of these 

 bodies. This is at present believed to be 

 the maximum record. What is to become 

 of this numerous family is one of the serious 

 questions of this day. The complete inves- 

 tigation of the theory of one is almost the 

 work of a lifetime. 



Of satellites, or secondary planets, seven 

 have been added to the list during the cen- 

 tury, one of Saturn, by Bond of Cambridge, 

 September, 1848 ; one of Neptune, by Las- 

 sell, soon after the discovery of the planet 

 itself ; two of Uranus, also by Lassell, 1851 ; 

 two of Mars, by Hall, of Washington, 

 August, 1877; one of Jupiter, by Barnard, 

 of the Lick Observatory, September, 1892. 

 We should perhaps include an eighth in this 

 category, an additional satellite of Saturn 

 having been announced by W. H. Pickering 

 two years ago, but as it has not yet been 

 confirmed, judgment must be suspended for 

 the present. 



The periods of rotation of Mercury and 

 Venus were investigated by the German 

 astronomer Schroeter, sometimes called the 

 Herschel of Germany, near the beginning 

 of the century. His conclusion was that 

 the length of the day on both these planets 

 differs but little from our own. These re- 

 sults kept their places in the text-books al- 

 most unchallenged until near the close of 

 the century. The multiplicity of observers 

 equipped with instruments greatly superior 

 to those of Schroeter were apparently un- 

 able either to confirm or disprove his 

 conclusions. In 1889, however, Schia- 

 parelli found what he considered decisive 

 evidence showing that the planet Mercury 

 rotates on its axis in the same time re- 

 quired to complete a revolution about the 

 sun, thus like our moon always keeping 

 the same hemisphere presented to the pri- 

 mary body. Later Schiaparelli came to 



