xiv.] FORBES' SCIENTIFIC WORK. 471 



the constant difference of one such unit. Now, the fact 

 to which M. Struve originally called attention, and on 

 which we believe all astronomers are agreed, is, that the 

 first of these groups is out of all proportion richer than 



i of the others, and that the numbers degrade in the 

 groups adjacent with excessive rapidity ; so that, for 



tuple, calculating on the numbers given by Struve, 

 we find the first group to contain 180 cases ; the 

 next three 68, or on an average 22 each; the next 



Ive 70, or six each on an average ; and the next forty- 

 eight only 94 in all, averaging two to each, while a 

 general average would assign only one star to 540,000 

 such units of area. The case, then, is parallel to that of 

 a target of vast size, marked out into 6,700 millions of 

 equidistant rings, riddled with shot marks in the bull's 

 eye, and with a tolerable sprinkling in the first 50 or 

 60 rings, beyond which the whole area offers nothing for 

 remark indicative of any particular local tendency, 

 though dotted all over uith marks, in the sparing 

 manner above described. Anyone who could view such 

 a target, bearing in mind what is said above, must 

 feel convinced that a totally different system of aiming 

 had been followed in planting the interior and exterior 

 balls. Such we conceive to be the nature of the argu- 

 ment for a physical connection between the individuals 

 of a double star prior to the direct observation of their 

 orbital motion round each other. To us it appears con- 

 clusive ; and if objected to on the ground that every 

 attempt to assign a numerical value to the antecedent 

 probability of any given arrangement or grouping of 

 fortuitously scattered bodies must be doubtful, we reply 

 that if this be admitted as an argument, there remains 

 no possibility of applying the theory of probabilities to 



registered ia< is whatever. We set out with a cer- 



hypothesis as to the chances, granting which, we 



the probability not of one certain definite 



arrangen hid) is of no importance whatever, but 



of certain ratios bein^ found to subsist brtwrcii the cases 



rt;iin piv.li- nn an ; at numbers. 



