THE SATELLITES OF MARS. 495 



known however, what connection exists between the comets and the meteors 

 though it appears that the latter have paths as eccentric as those of the 

 comctic orbits, and hence it is deduced that the earth encounters no less 

 than 56 meteor systems, thus affording proof that the total number of these 

 systems in the universe must be estimated by billions. 



It will readily be seen that a knowledge of the elements of the paths 

 described by the meteors is of considerable astronomical im2:)ortance. 

 While, as already stated, the general direction or radiation is from the 

 constellation Leo. it has been observed that often on the same night many 

 distinct centers of radiation may be traced. It is by the determination of 

 these centers that the elements above referred to may be calculated. Then 

 by comparing the results with the elements of the orbits of known comets, 

 it becomes possible to discover which comets, by rupture, according to one 

 theory, probably gave rise to the various groups of shooting stars. Hence 

 observations made with the naked eye, which fix the exact point in the 

 heavens whence the meteors appear to radiate, may prove of value. 



It is necessary first to note the region of the heavens whence the meteors 

 appear, and then specially to observe those bodies which seem to have the 

 shortest trajectories. These will, of course, be the ones nearest the center 

 of radiation, and in this w^ay the location of the latter can be quite accu- 

 ratel}'- determined. Look also for a pale light something similar to the 

 aurora, which is often present about the radiating point. It is also useful 

 to note the color and brilliancy of the meteors. The latter may be esti- 

 mated by comparison with Jupiter and Yenus, the brilliancy of these j)lan- 

 ets being taken as the maximum. If the meteors leave a trail behind them, 

 note the fact, and also observe how long the trail remains visible after the 

 star disappears, also whether it has any backward motion. A field glass 

 may be advantageously employed to recognize any special peculiarities of 

 the trail. These observations, if carefully made, will be accepted at any 

 astronomical observatory. Meteors also appear from the 27th to the 29th of 

 JSTovomber, and from the 6th to 13th of December, but not in such numbers 

 as upon the above mentioned dates. — Scientific American. 



The Satellites op Mars. — Since our article on this subject was in type, 

 wo have received the following note from Dr. Eobert Eeyburn, of Wash- 

 ington, D. C. : " In the recent accounts of the discovery of the satellites 

 of Mars, we have not seen any reference to the curious fact of the announce- 

 ment of their existence by Dean Swift in his celebrated satire, 'A Yoyage 

 to Laputa,' published in 1726. It may be found in the third chapter of that 

 work, and reads as follows: 'They have likewise discovered two lesser 

 stars or satellites which revolve about Mars, whereof the innermost is dis- 

 tant from the j)rimary planet exactly three of his diameters, and the outer- 

 most five ; the former revolves in the space of ten hours, and the latter in 



