IN CASES OF LEGAL EVIDENCE. 147 



series are so, as the inference is or is not a necessary one: and the numerical values of the com- 

 ponent fractions, or of their limits being assigned a nunieiical measure of the probability of the 

 accusation being true, or of its inferior limit, will be obtained ; and the evidence will or will not 

 warrant conviction as this number does or does not exceed the certain prescribed value; and 

 whether the precise value be or be not definitely assigned, that is, whether the probability be defi- 

 nite or indefinite, will be immaterial, so long as this condition is fulfilled. 



In civil cases, the questions to be decided having been elicited by the parties in their pleadings, 

 the value of the evidence by which they are to be determined is estimated in the same way ; 

 but it will frequently be necessary to assign the numerical values with greater accuracy. The 

 following paragraph applies to such cases, and seems also to involve an admission of all that is 

 contended for in favour of scientific investigation. " In some instances, nevertheless, where from 

 paucity of circumstances the usual means of judging of the credit due to conflicting witnesses fail, 

 it is possible that the abstract principles adverted to may operate by way of appro.^iimation, 

 especially in those cases where the decision is to depend on a mere preponderance of evidence " 

 Starkie 554. A paucity of circumstances or incompleteness of data is what distinguishes the evi- 

 dence in favour of events which are merely probable, from that which supports those which are 

 certain, and it is the business of the science to determine the probability of the truth of the event 

 from the data which are offered to support or disprove it, however limited in extent these data niav 

 be. When the numerical measure of this probability is precisely 1, the dala are insuflicient for 

 decision, and in no other case ; in criminal cases, this punctum indifferens is claimed by the legal 

 presumption in favour of innocence. 



If, therefore, in a case where the mere preponderance is to decide, we obtain a result by- 

 assigning to the probabilities which favour the claim of A the least values of which in our judg- 

 ments they are capable, and to those which favour the claim of B the greatest values of which 

 in our judgments they are capable; and another result, from the greatest which favour .^'s claim, 

 and the least which favour JB's ; then if each of these exceed ^, the decision is in favour of A, 

 and if each be less than ^, in favour of B \ but if one be greater and the other less than A, 

 more accurate values must be assigned to the numerical limits, till both the limiting values of the 

 probability be made to exceed or fall short of ^, or till on assigning what in our judgments are 

 correct values, a result precisely equal to ^ is obtained; in which latter case no decision can be 

 arrived at. The only peculiarity tiien in a case whose decision must depend on a mere prepon- 

 derance of evidence is this, that a more accurate estimate of the probabilities it involves must be 

 made. 



A consideration of the investigations by which these remarks are illustrated, will shew that the 

 mode of estimating the force of evidence employed in a court, is a process which algebraic investi- 

 gation analyses, and of which it explains the theory ; and an approximation, (in most cases, scien- 

 tifically speaking, a rude one,) to a result which is obtained with accuracy by assigning numerical 

 values to the algebraic symbols. The complication which exhibits itself in the algebraic process is 

 in the nature of the subject, and is not in any degree introduced by the operation employed. 

 The difficulties are difficulties which belong to the act of in any way eliciting truth from a compli- 

 cated series of circumstances; the practical process, to a certain extent, evades, and necessarily evades, 

 these; the algebraic encounters then), and resolves them into their elements. The employment 

 of symbolical language facilitates the processes of deductive reasoning, but docs not change them ; 

 the assigning of numerical measures to the probabilities involved defines with accuracy their mag- 

 nitudes, but in nowise modifies them. 



Again, the analytical process does not exclude considerations other tiian those which result from 

 the bare probabilities. Presumptions of law may be adopted in its formulae, and these may be 

 dictated by reasons of |)()licy, or other motives, as well as by the necessity for substituting a])proxi- 

 mations in j)racticc. They are inferences to wiiicii legislative enactment or judicial decision has 

 attached the legal consequences which properly belong to facts, and analysis therefore assigns to 

 them the measure of certainty. At the commencement of a criminal proceeding the law presumes 

 Vol. VIII. Pakt II. U 



