304- Notices respecting New Books. 



Iapetus, Titan, Rhea, Dione, Tethys, Enceladus, Mimas. The 

 reasons for the selection are set forth in a note which we transcribe 

 at length. 



" As Saturn devoured his children, his family could not he assem- 

 bled round him, so that the choice lay among his brothers and sisters, 

 the Titans and Titanesses. The name Iapetus seemed indicated by 

 the obscurity and remoteness of the exterior satellite, Titan by the 

 superior size of the Huygenian, while the three female appellatives 

 class together the three intermediate Cassinian satellites. The mi- 

 nute interior ones seemed appropriately characterized by a return to 

 male appellatives, chosen from a younger and inferior (though still 

 superhuman) brood. Should an eighth satellite exist, the confusion 

 of the old nomenclature will become quite intolerable. I am not 

 aware that a distant satellite of Jupiter (analogous to Iapetus and 

 our moon) has ever been looked for. Would it not be worth a 

 search?*" — P. 415. 



The contents of the present chapter may be briefly described. The 

 author first gives some explanations respecting the mode in which 

 the observations were made. A table follows, exhibiting a synopsis 

 of all the measured (and some of the estimated) angles of position of 

 the satellites as taken both with the equatorial and reflector. In 

 order to render the observations available for the purpose of affording 

 epochs by which to correct the received periodic times, the observed 

 angles of position must be converted into Saturni centric longitudes. 

 Formula? and elements for this purpose are given ; but as the use of 

 the elements supposes the orbits of the satellites to be coincident 

 with the plane of the ring, they are not applicable to the reduction 

 of the observations of Iapetus, the orbit of which deviates from that 

 plane very considerably. Of Mimas, there being only a single ob- 

 servation, no conclusion could be deduced respecting the orbit. In 

 respect of the remaining five satellites, tables are given exhibiting 

 the Saturnicentric longitudes from the descending node of the ring, 

 calculated from the elements and formulae above referred to for each 

 of the times of observation, and for each satellite drawn out seriatim. 

 These observed longitudes are then compared with the corresponding 

 mean longitudes, calculated from certain assumed epochs of longitude 

 and mean motions, and the differences given. In most cases, where 

 the differences are considerable, the observations were found to have 

 been recorded as doubtful or unsatisfactory, and some of them are 

 therefore rejected. In order to deduce elements, the observations 

 were treated by a method of graphical projection, and the results 

 gave values of the eccentricity, the equation of centre, the perisatur- 

 nium, and correction of epochs for four of the satellites, viz. Titan, 

 Rhea, Dione, Tethys. For Enceladus the correction of the epoch 

 only was obtained. 



• It may not be out of place to remind the astronomical reader that 

 mythological names were long ago proposed for the satellites of Jupiter by 

 Simon Marius — the same who disputed with Galileo the honour of their 

 discovery. The names proposed by Marius were those of Jupiter's cup- 

 bearers — Io, Europa, Ganymede and Callisto. 



