144 Double Stars. 



as a double, or, in some cases, triple, quadruple, or multiple 

 star. If, however, their mutual distance is sufficient to admit 

 of their being separately distinguished by the naked eye, they 

 are seldom classed under these titles, which are, generally 

 speaking, reserved for those too close, as well as in many cases 

 too minute to be seen without a telescope. Of such it has been 

 computed that there may be about 6000 in the heavens (in- 

 cluding of course both hemispheres), and as many of them are 

 especially interesting objects of telescopic research, it is in- 

 tended in the present paper, and others which will form its 

 continuation, to give some plain directions which may enable 

 amateurs to find them readily, and view them to advantage. 



But in the first place it maybe asked, what peculiar interest 

 do stars acquire from being thus brought into juxtaposition ? 

 In many cases it may be answered, that the mere comparison of 

 magnitude, or contrast of colour, thus brought out, is both 

 singular and beautiful, and will well repay the slight trouble of 

 the search. But others possess a higher claim upon our atten- 

 tion. In many instances they are not merely supposed, but 

 ascertained to be systems of connecting suns, bound together 

 and revolving round each other by the same combined action 

 of gravitating and propulsive force which governs the motions 

 of our solar system, and is thus proved to pervade the nearer 

 regions, and must by analogy be supposed co-extensive with 

 the whole domain of the starry universe. Such pairs of stars 

 are called binary, to distinguish them from those whose duplicity 

 is only optical or apparent ; the mere accidental consequence of 

 their lying behind each other in a line passing nearly through 

 the observer's eye. This distinction cannot be demonstrated 

 by a single observation, however accurate, but may be effected 

 in two different ways, by examinations repeated after sufficient 

 intervals of time. In many instances, as experience will readily 

 show, the very aspect of a pair is enough to point out the pro- 

 bability of its physical relation. The components are frequently 

 so curiously alike in physiognomy, if we may so apply the term, 

 that their family connexion is all but self-evident ; and the 

 chances are exceedingly small that in such a case one object 

 should be found almost exactly in a line with another, whose 

 difference in size is so precisely balanced by a corresponding 

 difference in distance, as to produce the effect of equality. 

 Still this, though a very high probability, does not amount to 

 actual demonstration, which can only be obtained, as we have 

 said, in one of two ways. Either we may observe such a change 

 from time to time in the relative position of the two stars, as 

 actually to exhibit their revolution to the eye ; or we may find 

 them, after the lapse of years, though Bensibly unmoved with 

 respect to each other, get both gradually displaced through 



