But although the law is thus liberal in looking through mere form, in order to see the real substance of the questions raised, a positive variance or discrepancy between a pleading and the proof adduced in support of it is fatal,— a rule considered necessary to prevent the opposite party from being unfairly taken by surprise, and the whole system of pleading converted into a snare.® 6. The student should here consult the statutes concerning amendments. PART II. THE SECONDARY RULES OF EVIDENCE. The secondary rules of evidence are those rules which relate to the modus probandi, or mode of proving the matters that require proof. The fundamental principle of the common law on this subject is, that the best evidence must be given, — a maxim the general meaning of which has been explained in a former part of this work.1 In certain cases, however, peculiar forms of proof are either prescribed or authorized by statute. The whole matter may be treated in the following order: 1. Direct and Circumstantial Evidence. 2. Presumptive Evidence, Presumptions, and Frictions of Law. 3. Primary and Secondary Evidence. 4. Derivative Evidence in general. 5. Evidence supplied by the Acts of Third Parties. 6. Opinion Evidence. 7. Self-regarding Evidence. 8. Evidence rejected on Grounds of Public Policy. 9. Authority of Res Judicata. 10. Quantity of Evidence required. 1. Book 1, pt. 1, ante. [477] CHAPTER I. DIRECT AND CIRCUMSTANTIAL EVIDENCE. ALL judicial evidence is either direct or circumstantial. By" direct evidence" is meant when the principal fact, or factum probandum, is attested directly by witnesses, things, or documents. To all other forms the term "circumstantial evidence" is applied; which may be defined, that modification of indirect evidence, whether by witnesses, things, or documents, which the law deems sufficiently proximate to a principal fact, or factum probandum, to be receivable as evidentiary of it. And this also is of two kinds, conclusive and presumptive: "conclusive," when the connection between the principal and evidentiary facts the factum probandum and factum probans1— is a necessary consequence of the laws of nature; as where a party accused of a crime shows that, at the moment of its commission, he was at another place, &c.: " presumptive when the inference of the principal fact from the evidentiary is only probable, whatever be the degree of persuasion which it may generate. As regards admissibility, direct and circumstantial evidence stand, generally speaking, on the same footing. It might at first sight be imagined that the latter, especially when in a presumptive shape, is inferior or secondary to the former, and that, by analogy to the principle which excludes second-hand and postpones secondary evidence, it ought to be rejected, at least when direct evidence can be procured. The law is, however, otherwise. Circumstantial evidence, whether conclusive or presumptive, is as original in its nature as direct evidence: both are distinct modes of proof, acting as it were in parallel lines wholly independent of each other. Still, the non-production of direct evidence which it is in the power of a party to produce is 1. The fact to be proved and the fact that proves. matter of observation to a jury, as indeed is the suppression of any sort of proof.2 Direct and presumptive evidence (using the words in their technical sense) being, as has been shown, distinct modes of proof, have each their peculiar advantages and characteristic dangers. Abstractly speaking, presumptive evidence is inferior to direct evidence, seeing that it is in truth only a substitute for it, and an indirect mode of proving that which otherwise might not be provable at all. Hence, a given portion of credible direct evidence must ever be superior to an equal portion of credible presumptive evidence of the same fact. But in practice it is from the nature of things impossible, except in a few rare and peculiar cases, to obtain more than a very limited portion of direct evidence as to any fact, especially any fact of a criminal kind; and with the probative force of such a limited portion of direct evidence, that of a chain of evidentiary facts, forming a body of presumptive proof, may well bear comparison.3 2. 1 Stark's Ev. (3d Ed.) 578; id. (4th Ed.) 874; Chamberlayne's Best's Evidence, 276, 277; 3 Chamberlayne on Evidence, § 1712 and note 3. 3. See next note ante. CHAPTER II. PRESUMPTIVE EVIDENCE, PRESUMPTIONS, AND FICTIONS OF LAW. The elements, or links which compose a chain of presumptive proof, are certain moral and physical coincidences, which individually indicate the principal fact; and the probative force of the whole depends on the number, weight, independence, and consistency of those elementary circumstances. A number of circumstances, each individually very slight, may so tally with and confirm each other as to leave no room for doubt of the fact which they tend to establish.1 Thus, on an indictment for uttering a bank-note knowing it to be counterfeit, proof that the accused uttered a counterfeit note amounts to nothing or next to nothing, any person might innocently have a counterfeit note in his possession, and offer it in payment. But suppose further proof to be adduced that, shortly before the transaction in question, he had in another place, and to another person, offered in payment another counterfeit note of the same manufacture, the presumption of guilty knowledge becomes strong.2 It is, however, of the utmost importance to bear in mind, first, that, if all the circumstances proved arise from one source, they are not independent of each other; and that an increase in the number of the circumstances will not in such a case increase the probability of the hypothesis: secondly, that, where a number of independent circumstances point to the same conclusion, the probability of the justness of that conclusion is, not the sum of the simple probabilities of those circumstances, but the compound result of them: and lastly, that, the circumstances composing the chain must all be consistent with each other.3 1. See Richardson's Case, Chamberlayne's Best's Evidence, Appendix No. 1. 2. See 4 Chamberlayne on Evidence, § 3225; Rex v. Green, 3 Car. & K. 209; Chamberlayne's Best's Evidence, 281, 282 and note. 3. Chamberlayne's Best's Evidence, |