EVIDENCE. 316 statement is incidental to the event itself, and to some extent, characterizes or explains it. Thus on the murder trial of a defendant it is proper to prove a statement made at the time of the homicide by any person present, which tended to show that the defendant committed the homicide or that the act was intentional or malicious. There are some other exceptions to the hearsay- evidence rule., but these are of infrequent occur- rence and of comparative unimportance, and do not admit of discussion here. III. Eeal Evidence, Writings. Legal evidence is not limited to the sworn testimony of wit- nesses. Specific objects, when properly identi- fied by oral testimony, may often be introduced in evidence when their very existence or their character or appearance tends to prove or dis- prove an alleged fact. Thus models, parts of machinery, weapons, clothing, etc., may be in- troduced in evidence. Such evidence cannot of course be submitted to an appellate court as a part of the record of the trial, and for that reason the extent to which such evi- dence may be received may be limited within the discretion of the court, and in some jurisdic- tions practically no such evidence is admitted. Writings or documents may generally be intro- duced directly in evidence for the purpose of proving the truth of statements contained in them. At common law documents purporting to be more than thirty years old required no particular authentication, or, as was said, such documents proved themselves. The execution of other documents must, however, be proved by the sworn testimony of a witness to the execu- tion, or, if he be dead, by proof of the handwrit- ing of the person who executed the document. The so-called best-evidence rule applies to docu- mentary evidence. Briefly stated, it is that the best evidence of the contents of a document is the document itself, and that no other evidence of the' contents of a written instrument is ad- missible. This rule is subject to many exceptions. real or apparent. Thus: (a) Where the original document is in duplicate form any one of the duplicates may be introduced in evidence as an original, (b) Secondary evidence (i.e. a copy or oral testimony) of a writter. notice is admissible, (c) Matters of public record may be proven by secondary evidence, in most jurisdictions by a certified copy of the record, (d) Secondary evi- dence may also lie introduced to prove an instru- ment which has been lost or destroyed, or when- ever the other party to an action, having the document in his possession, fails to produce it at the trial for the purpose of preventing its being introduced in evidence on due notice. One who has willfully destroyed a document will not. how- ever, be allowed to give evidence of its content-. When proof of a document is offered but for tin' purpose of proving the truth or untruth of any statement contained in it, it is real evidence, as distinguished from a writing: and the best-evi- dence rule should and probably does ii<>t apply. The common-law rule a- to proof of documents has been much modified by statute. In mosi jurisdictions all documents attested before a no- or corresponding officer are prima facie ad- missible in evidence if relevant. IV. Tut: Parch Evtdi mi: Rote. This is prop- erly a rule of substantive law which is. in effect, i hat die iei mi . ,i .1 contract or other legal instru I should he deemed I" be embodied wholly in EVIDENCE. the written instrument executed by the parties thereto, or, stated in terms of evidence, the rule is that parol or oral evidence shall not be intro- duced for the purpose of varying the terms of a written instrument. The rule, though necessarily subject to many exceptions, is founded upon the just notion that when parties have deliberately embodied their agreement or transactions in writ- ing, they should not thereafter be allowed to dis- pute its terms. The following are the most im- portant cases in which to vary the express terms of a written instrument testimony may be given : la) Where the parties did not intend to re- duce all the terms of the agreement to writing. (b) When the writing or agreement is varied by a subsequent parol agreement. (c) When the evidence is introduced to show that the written instrument has never taken effect because of the non-occurrence of some agreed condition precedent. (d) When a term of the instrument is ambigu- ous and parol evidence is necessary to explain the meaning, and upon analogous grounds where the term of a written instrument has a technical or local meaning requiring oral explanation. (e) When the proof of a custom which is in law a part of a contract or other document varies the effect or meaning of the written lan- guage. (f ) When in equity an action is brought to re- form or rescind a written instrument, or construe a conveyance as a mortgage. V. Opinion Evidence. In general witnesses are allowed to testify only as to facts, and not as to their inferences or opinions based upon facta within their knowledge. To permit, the witness to indulge in opinion testimony would be a usurpa- tion of the function of the jury, whose duty it is to draw inferences of fact and to form an opin- ion, where an opinion is necessary to the verdict. Thus the witness, when the facts of a conversa- tion are in issue, must testify as to the terms of the conversation and not his conclusions as to its meaning. There are, however, three impor- tant exceptions to the rule that opinion evidence is inadmissible. They are: (a) Matters of com- mon experience ; matters of common knowledge to a certain extent the result of inference. Thus, to testify that a certain day was cold, or that a knife was sharp, involves the operation of the witness's mind in drawing a conclusion ; but since these are matters of common experience about which the conclusions of the witness are as trustworthy as those of a jury, such testimony is legally admissible as evidence, (b) Matters not of common experience, but about which the opinion of the witness is under the circumstances more trustworthy than any which could be formed by the jury. Thus, a witness may be so situated with reference to an event or combina- tion of circumstances as to be able to draw a more accurate conclusion from them than the jury, which should rely wholly upon verbal testi- mony about I he occurrence. Thus, the witness may be allowed to give his opinion of the distance between an annroaching street-ear and a pedes trian before warning of the approach was given: or. under certain circumstances, he may be al- lowed In give his opinion of the rate of speed at which the ear was moving. His presence at tin time of the event enables him to form a more accurate opinion than (be jury, which can only rely upon a necessarily imperfect description of
