138 Prof. Encke's Ephemeris q/' his Comet, 



very much with their proximity to the sun. Laplace has 

 adopted the number without alteration. In order to obtain 

 approximately the mass of Mercury, which has ftevcr yet been 

 determined, 1 have first substituted the most accurate values 

 of the other masses. Thanks to your excellent observations, 

 which are completely confirmed by Bessel (Bessel finds the 

 mass of Jupiter = tottbTt)' ^^ ^'"^ quite clear about the most 

 important of them, that of Jupiter. The others have a smaller 

 influence even if they are erroneous. I have then used a dou- 

 ble calculation. In the first I have assumed that, till 1835 in- 

 clusive, the earlier determined elements were quite accurate. 

 In fact the errors of 1832 and 1835 are. small. With this as- 

 sumption I have sought to remove the apparent error in 1838, 

 by an alteration of the mass of Mercury, and an alteration of 

 the constant of the resistance. This succeeded perfectly, and 

 I obtained a slightly changed constant of the resistance, and 

 a mass of Mercury = 3 otjy9TT' fibout f rds of the former mass. 

 In the second calculation I have endeavoured to remove the 

 errors of 1832 and 1835, as well as that of 1838 (each being 

 previously treated as if it had arisen from an erroneous time 

 of perihelion-passage), by an alteration of the same elements, 

 namely, the mass of Mercury, and the constant of the resist- 

 ance. Here remain likewise only small differences, if the con- 

 stant of the resistance is left quite unchanged, and the mass of 

 Mercury assumed at ^^gjyyT' ^^ about y^^^ths of that of La- 

 grange. This last determination I intend to adopt as a basis 

 for accurate comparison, and correct it more closely. It has 

 the truly remarkable peculiarity that with it the defisities ai'e 



tj = l-i'2 ? = 0-92 i = 1-00 S = 0-95 



= 0-25 T; = 0-24 T? = 014 ^ = 0-24 ; 



consequently the solar system appears to be composed of two 

 sets of bodies, whose densities are either nearly = 1, or = |, 

 and which are separated by the interval between Mars and 

 Jupiter, where there exists no large planet, but only the four 

 small ones. 

 Dec. 20, 1841. 



Ephemeris of the Periodical [Encke's] Comet, 1842. 



Elements. 



Epoch, 1842, April 12, 0*^, Berlin Mean Time. 



Mean Anomaly 359° 58' 34"-3 



Sidereal Daily Motion 1070"-61433 



Angle of eccentricity .... <p = 57° 39' 13"'8 {e = sin <p) 



Longitude of Perihelion 157 30 4-71 Mean Equinox of 



Longitude of ascending node . . 334 39 1-8/ April 12, 1842. 

 Inclination 13 20 248 



