172 SCENERY OF THE HEAVENS. 



know. Minute white specks appear in the neighbourhood of the stars, y Hydrae, K 

 Geminorum, and t Ursse, which in all likelihood are their encircling planets tributary 

 companions plainly and vastly inferior, according to the analogy of subservient bodies 

 in our system. Their intervention would have no perceptible effect upon the 

 appearance of their primaries to our vision. The most probable hypothesis that has 

 yet been proposed to account for the examples before us of stellar changeableness is 

 that of axical rotation. The variable stars are supposed to have parts of their surface 

 less luminous than the rest, which when presented to us in the course of rotation produce 

 the periodical decay of light, and absolute invisibility observable. A variety of circum- 

 stances occur to favour this idea. Rotation upon an axis is a law to which every orb is 

 subject, with which we are sufficiently acquainted as the sun, the planets, and their 

 satellites. The greatest uniformity marks the execution of the law, and in this it differs 

 from translation in space. The planets travel in irregular paths and with varying 

 velocities in their orbits, but their axical motion is uniform. If, therefore, one of the 

 hemispheres of a rotating body within the sphere of vision should be less luminous than 

 the other, periods of decay, obscurity, revival, and vivacity, would be exhibited, of 

 uniform occurrence and duration. Now, those who have paid most attention to solar 

 phenomena are of opinion, that besides the sun having variable spots upon his disk, which 

 at times have been so numerous and extensive as to impair his orb, there is reason to 

 believe the illuminating power of his two hemispheres to be unequal, one being much 

 fainter than the other. We may not be sensible of this, because, comparatively situated 

 in immediate vicinity to his effulgence ; but, removed to a vast remoteness, his rotatory 

 motion might constitute him sensibly a variable star to us. Herschel remarks : " The 

 rotary motion of stars upon their axes is a capital feature in their resemblance to the 

 sun. It appears to me now, that we cannot refuse to admit such a motion, and that 

 indeed it may be as evidently proved as the diurnal motion of the earth. Dark spots, or 

 large portions of the surface less luminous than the rest, turned alternately in certain 

 directions either towards or from us, will account for all the phenomena of periodical 

 changes in the lustre of the stars so satisfactorily, that we certainly need not look out for 

 any other cause." 



We now proceed to notice the Multiple stars a class unknown until a very recent 

 date. Soon after the application of the telescope to the heavens, it was perceived that 

 some of those brilliant points, which appear single stars to the naked eye, are in reality 

 stellar combinations comprising two or more individuals. But little attention, however, 

 was paid to them, and no suspicion entertained of their numerical amount. Dr. Hook, 

 referring to y Arietis, states : " Of this kind, the most remarkable is the star in the left 

 horn of Aries, which, whilst I was observing the comet which appeared in the year 1664, 

 and followed till he passed by this star, I took notice that it consisted of two small stars 

 very near together; a like instance to which I have not else met with in all the heavens." 

 It was reserved for the elder Herschel to detect the richness of the mine, and to take pre- 

 cedence in bringing some of its treasures to light. A catalogue of five hundred stars, 

 apparently single, but in fact binary, was produced by this distinguished observer, and 

 presented to the Royal Society ; and, when he ceased from his labours, his mantle fell 

 upon successors worthy to receive it. The list of conjoined bodies, whose positions and 

 relative distances have been accurately determined, now includes a number which is five 

 or six times greater than that which appears in the general stellar catalogue of the ancient 

 observers. Sir James South and Sir John Herschel produced a catalogue of 380 multiple 

 stars in the year 1824, as the result of their joint labours. This was followed by one of 

 480 from South, and another of 3300 from Herschel the fruits of solitary observation. 

 M. Struve, of Dorpat, also has registered the data of 3000. These are all included in the 



