410 SCIENTIFIC RECORD FOR 1883. 



URANUS. 



Signor Schiaparelli, the director of the Eoyal Observatory at Milan, 

 gives in AstronomischeNachrichten, No. 252G, the results of a series of ob- 

 servations of the figure of the planet Uranus, which has been exception- 

 ally favorably situated for that purpose. His results (as to the amount 



of oblatenets), by two separate methods, are 1(J 98 , Q g 3 and fo 94 ■ 67 



agreeing very well with that obtained in 1842 and 1843 (the last time 

 when the planet's position was equally favorable) by the late Professor 

 Madler from his observations at Dorpat, and indicating that Uranus is 

 the most elliptical of all the planets excepting Saturn. A similar 

 result has been reached by Professor Young with the Princeton re- 

 fractor. 



Mass of a planet from observation of two satellites. — M. Struve recom- 

 mends measurement of the position angle and distance of a satellite 

 from another satellite, and not from the primary planet. A series of 

 such measurements on satellites of Jupiter has been begun at Pulkova. 

 The observations occupy one-third the time, and are considered to be two 

 or three times as accurate as those by direct reference to the center of the 

 planet. They are free, moreover, from the unknown constant errors 

 inseparable from the latter — an advantage which Prof. A. Hall, in 

 this paper, considers cheaply purchased at the price of greater difficul- 

 ties in computation. He shows that while the solution of 6 normal 

 equations requires 77 auxiliary quantities, that of 12 (the elements of 

 both orbits being involved by the new method) requires 442, and there- 

 fore nearly six times the labor. But these 12 equations give the period 

 and mean distance of each satellite, and hence two values of the planet's 

 mass. (Phil. Soc. Wash., math. sect. ; meeting April 26.) — (Science.) 



COMETS. 



The Comet of 1771. — The comet discovered by Messier at Paris on 

 April 1, 1771, and last observed by St. Jacques de Silvabelle at Mar- 

 seilles on July 17, has long been mentioned in our treatises on astron- 

 omy as undoubtedly moving in a hyperbolic orbit. This inference was 

 first drawn by Burckhardt, who considered that of all the comets cal- 

 culated up to the time he wrote (M6moires pr^sentes par Savans etran- 

 gers, 1805) that of 1771 was the only one of which it could be stated 

 with some degree of certainty that the orbit was hyperbolic. Encke 

 reduced anew the six observations employed by Burckbardt, and found 

 that the most probable elements were hyperbolic with eccentricity = 

 1.00937, which is almost identical with Burckhardt's value (1.00944). 

 Nevertheless he did not regard the decided superiority of the hyper- 

 bola in the representation of the six places as an indubitable proof of 

 the necessity of admittiug motion in that curve; the positions used 

 were not normal positions, but the results of single and isolated ob- 



