IN CASES OF LEGAL EVIDENCE. 155 



person being convicted ; but it must be either by increasing the chance of a guilty person escaping, 

 or by rendering the practical process more i)erfect ; if we were to conceive the elementary proba- 

 bilities to be elicited by the skill of science, and presented to the jury as separate issues, they would 

 then have to decide on simple facts instead of on complex series of facts, and the remainder of the 

 process would be logical deduction, and therefore would exclude the possibility of error. A result 

 so obtained would possess all the accuracy of which the subject is capable: by as much as the prac- 

 tical process differs from this, by so much is it, as far as mere accuracy is concerned, inferior : the 

 difference is the price of practicability. 

 In the value of it, 



10 100 u I 



11 101 2a -a^ 500^ 



Then -i_2p,.Ai>> — , 



p, A, ^' ' ^ 1000 



For determining the value of tto. 



1000 



and TT, <t . 



1111 



1 1 1 /I \ 1 a \ 



First, Q = — — 2AiP,, --l> <|:0; (--l)> ^O: — - — >_<to. 



1 '^ u ^ 200^ ' \v ;/ ^100^ ' 2o-a. 100^ 



The values of it and v being assigned independently of this particular allegation. 



Then _L2^p,>.'°' 



A, Pi ' ' 20000' 

 and e<t->>l, f<\>l, 



J ' ^1. ^ '^^ ^ 2500 



and -. — j2A,p> . Q <t 



h,pAe+f{l-e)\ "^'-^^2500' ^^2543- 



Since Q differs so little from 1, the values of u and v are not materially diminished by the 

 evidence as to this collateral fact. 



1 11 a 1 



Assuming, therefore, 1 = -- , and — 1 = w , — = — . 



^ U 200 V 2a - a 100 



43 100 + a? (20000 + 99) 

 2500 ~ 20000 + w ' 



whence a? >■ — . 

 82 



Employing then this value of 1 in the expression for ttj, which is 



'""T — ~, ) — ^*'^" 



1 " 1 , ^i . I 



and putting = — , and — ■i — , 



' ^ 2a-a 50' A, ^100' 



Vol. VIII. Paut II. 



