and the Variable Stars. 361 



it to the regions from which it was withdrawn. In like manner, 

 large planets have the power of concentrating the jetherial me- 

 dium in the regions over which they move; especially when their 

 orbits are so wide, and the movement of the system so rapid, 

 that their tracks in space deviate little from a straight line. 



Had the planets moved in planes coincident with the line of 

 solar motion, the columns of dense fether which the larger ones 

 leave behind them, would alternately pass over the sun and cause 

 a perceptible augmentation of his brilliancy. In many of the 

 distant systems, the track of the central body has so small an 

 inclination to the planes in which its attendants revolve, that 

 each of these bodies takes some part in maintaining the great 

 fire by which they are warmed and illuminated. The stars 

 X Cygni and Mira exhibit, in their change of magnitude, the 

 peculiar phjenomena which might be expected to result from 

 such an arrangement. The mean time which the former star 

 occupies in its course of variation has been estimated at 406 

 days ; but it sometimes differs several days from this amount ; 

 and in its maximum brightness it varies from the fourth to the 

 seventh magnitude. It appears, however, that these irregu- 

 larities are most decided after a lapse of 8^ and 100 periods of 

 variation ; and Argelander shows that its changes may be calcu- 

 lated with tolerable accuracy by a formula similar to those used 

 for the determination of planetary pertui-bations. The variable 

 splendour of this distant sun must be ascribed to the influence 

 of three planets; one revolviiig around it in 406 days, another 

 in 3451 days, and the third in 40,600 days; and being confined 

 to planes which pass close to the line of. the proper motion of 

 the central luminary, are enabled to affect the development of 

 his light. The eftects of planets in condensing the fetherial con- 

 tents of space, is also indicated by the fluctuating brilliancy of 

 Mira ; for though there are great inequalities in the time and 

 the degree of its variation, they are periodical in their occurrence, 

 and seem to be regulated by determinate laws. 



Of the other variable stars, the greater part are in like man- 

 ner characterized by such irregularities as might be expected to 

 arise from the action of a plurality of worlds which attend them. 

 In considering the conditions which planetary atti-action requires 

 to produce such effects, it would seem that the members of other 

 systems, like those of our own, have the planes of their orbits 

 confined to a limited range. There is, indeed, a great regularity 

 in the decline and return of brightness in some stars of short 

 periods of variability; but in these cases the effect nmst be 

 mainly dependent on the presence of a large jilanet which re- 

 volves in a small orbit, and alters, in a sensible degree, the 

 attraction of the central sphere. Though this alteration might 

 Phil. May. S. 4. Vol. 15. No. 101. May 1858. 2 B 



