xiv.] FORBES' SCIENTIFIC WORK. 476 



position ? and is the earth at present in that position ? 

 These two last questions would be excessively impro- 

 bably answered in the affirmative if we merely knew 

 that there are stars and an earth in space ; and therefore 

 tlif supposition that the individuals of many of the 

 double stars are far from one another as compared with 

 their distances from the earth is d priori excessively 

 improbable. I scarcely think the calculations which 



e been made have any reference to the probability of 

 an answer to either of these subsidiary questions or of 

 Question 1, but I am not confident in this opinion. 

 They all, so far as I know, relate to subjects of which 

 the scattering of sand upon a surface, from a sieve, 

 which you adduced, is an illustration, but I doubt 

 whether the three dimensions of the geometrical question 

 have been properly taken account of. 



' Question 2 gives rise to some excessively curious con- 

 siderations regarding the motion of a system of points 

 acting on one another according to Newton's law. Will 

 it not be only in special cases that any two will ever 

 come to be extremely near one another as compared 

 with their distances from the others, unless they are so 

 initially ? Again, it is certainly only in a special case 

 that a pair, at any time far asunder, shall come to be 



, near, and that another pair shall come to be very 

 at the. same time ; and that numerous pairs may 

 come to be very near, two and two, at the same time, is 

 still more special. Hence it is excessively improbable 

 that Question 2 could be answered otherwise than in the 

 allirmative. Would it not be altogether futile to at- 



;pt to estimate numerically this improbability? . . .' 



From BISHOP TERROT. 



\K PKOI KSSOR, 'EDINBURGH, October IQth, 1850. 



'. . . I was from home when Prof. Krllaml left 

 your ] tl August 30. I returned home and 



found it OD Oct"l,er >> ; this date I ha\v \\rillni on the 

 bark. I \uil 1. both of the letter and paj- 



