254 Prof. Encke on the Construction and Arrangement 



on which account the coordinates for those moments have not 

 been added. 



The occultations of the first two satellites are on the page 

 on the left ; those visible in Berlin are distinguished by an 

 asterisk (*). On the right hand are contained the times of the 

 superior geocentric conjunction with the corresponding ratio 



of the axis — , where a denotes the great, and b the small semi- 

 axis. The sign — signifies that the satellite has in the su- 

 perior conjunction a southern jovicentric latitude, or that we 

 see the southern part of the plane pf the satellite's orbit. The 

 sign + would accordingly denote the visibility of the northern 

 part of it. At the end of the column for each satellite will be 

 found the tables of reduction belonging to it. 



Their use may be learnt by the following example. Let it 

 be required to find the position of the two satellites for April 

 14th, 15 h 14/*2; then the next preceding geocentric conjunc- 

 tions are to be taken together with the value of ~ for the 

 given time. ^ ^ ^ ^ - h ^ _ Q ^ 



II. 13. 9 57*1 -63*7 



These deducted from the given time present the arguments 

 for the tables of reduction 



Sat. I. d l h 20'-7 

 II. 1 5 17-1 



For these we take from the tables 



Sat I. x = +1*13, 3/ =+5*59 

 II. = +7*55, = -5-01 



The latter ones (viz. j/ ) divided by — then give, with proper 



regard to the signs, these positions : 



Sat. I. x — +1-13, Sat. II. x — +7*55 

 y— —0-09. y = +0-08. 



Both x and y are expressed in radii of Jupiter ; x is the abscissa 

 on the great axis of the ellipsis of the satellite taken positively 

 in the direction of its motion or eastward ; y in the direction 

 of the jovicentric latitude, the northern one being positive. In 

 the field of the telescope a positive x will indicate the satel- 

 lite's position to the right of Jupiter, and a positive y its posi- 

 tion to the south of it. It appeared unnecessary to give the 

 angle which the great or small axis forms with a circle of 

 latitude or declination, as the belts of Jupiter sufficiently ex- 

 hibit the position of the great axis. 



For the third and fourth satellites the eclipses have not been 

 given, but instead of them the times of the middle of the eclipses 



taken 



