( 653 ) 



' 2a 



and from this finally for llie lot-us 



'11 if {a — x) 1= (3 x ~~ of ; 



1 



SO this is a cissoid, whose ciisp hes at a distance .r =: — r/ from 



Ö 



point () and whose asymptote passes tiirough jl 



()BSP]KVATI()N. The systems of eonies treated in these two 

 cases are simply intinite systems, where more than one ronie pass 

 through a point and more than one eoine touches a rii2;ht line ; so 

 they are distinguished from the ordinary [)encils and the tangential ones. 



Thus for the tirst mentioned system six conies pass through a 

 point and twelve conies touch a right line. 



Astronomy. — ''On the masses diid ('leiiiciits of Jxijdters SateUifps, 

 (iiul tlu' mass of tlw systeni', by Dr. W. J)K Sittkk. vCommn- 

 nicated by Prof. J. 0. Kapteyn). 



(Communicated in the meeting, of February 29, 1908). 



The determination of the elements and masses of the satellites of 

 Jupiter and of the mass and the dynamical compression of the planet, 

 which is communicated in the following pages, is based almost exclu- 

 sively on heliometric and photographic observations made at the obser- 

 vatories at the Oape of (lood Ho[)e, Pnlkowa and Helsingfors, in the 

 years J 891 to 1904. 



In addition to these I have also included in the discussion the 

 observations made by Bessel with the heliometer at Königsberg in 

 J 832 to 1839, and the values of the node of the second and the 

 perijove of the fourth satellile in 1750. (for which Dklambuk's values 

 were adopted). These laller have however, as will appear later on, 

 only a very slight effect on the final results. The determination of 

 all masses and elements is I hus practically independent of observations 

 of eclipses. 



Previous to 189J no series of observations of the satellites except 

 of the eclipses had been made with the purpose of deternuning the 

 elements of the orbits. Sncli series of observations as had been executed 

 in the first half of the nineteenth century by Hessel, x\iry and others, 

 were avowedly intended only lo determine the mass of .luj)iter. 

 ^Accordingly the satellites were by these astronomers, so far as possible. 



