An instance of this is when a man has by some statement or admission induced another with whom he was dealing to enter into a contract; he will not afterward be permitted to deny the truth of such statement or admission if the effect would be to work an injury to such third party. So a tacit admission, as when the owner of a chattel stands by while another sells it as his own, and neglects to give notice of his right; this will operate as an estoppel to his setting up his claim against the innocent purchaser. To this head also belongs what is called res judicata, that is to say, the rule that when a fact necessarily involved in an action is once determined it shall not afterward be called in question as between the same parties or persons claiming under them. A judgment or decree of a competent court is final not only as to what was actually determined, but as to every matter which was involved in the issue, and which could have been decided. The record of the judgment is the only proper evidence of what was in issue, and it cannot be proved aliunde that some matter was in fact involved and taken into consideration which does not appear by the record to have been involved in the issue. This is the rule as to decisions of tribunals in our own country.

In respect to foreign judgments and-decrees, the effect is the same when the court had jurisdiction of the case, and no fraud has been practised. The record itself, which must be produced, is not conclusive as to facts necessary to give jurisdiction, and a defendant will be permitted to prove that he was not personally served with process; so any fraud on the part of the court or its officers may be shown. But the regu-larity of the judgment having been established, | it is conclusive upon all matters embraced in the issue.-The fourth class in the arrangement we have made of our subject, viz., the comparative weight of evidence, is of a twofold character. Judicial discrimination may lead to the rejec-tion of testimony as being entitled to no weight at all, or it may determine the relative influence which it should have if admissible in the , decision of a question of fact. The former we have already considered, so far as respects the incompetency of witnesses and the exclusion of hearsay testimony. But evidence is sometimes excluded for reasons of more limited application.

Thus, inferior testimony is not admitted when a party has it in his power to produce what is of a higher order; as if the question be as to the title to real estate derived from a deed, the best proof will of course be the production of the deed itself, and no other proof will be admitted as a substitute, unless a satisfactory reason is given for its non-pr"oduc-tion, as where it has been lost or destroyed. But in this case, the substituted evidence must be exclusively as to the contents of the deed. But where under statutes providing therefor conveyances of real estate are recorded, the record or a certified copy is allowed to be read in evidence with the same effect as the original. So when a contract is in writing, it is necessary to produce the writing itself, and no other evidence can be given of the terms of such contract, without showing first the loss of the writing, or that for some other satisfactory reason it is impracticable to produce it; upon making which proof, parol evidence may be given as to the contents.

And whenever, in the course of a trial, a fact comes in question, the evidence of which is in writing, the same rule is applied, viz., that no other evidence can be admitted than the writing itself if in existence, and if not, then only the substituted proof of its contents. It may however happen that nothing more than the purport can be shown, and not the exact phraseology; and some latitude will be allowed in such case, as by admitting proof of the acts of parties, and other circumstances, but still having in view to get at what was expressed by the writing. It does not follow, however, that when the best or what is called primary evidence cannot be produced, inferior or what is called secondary evidence will in all cases be admitted. Thus, hearsay evidence is in general excluded, even if none better can be procured. Upon the same principle, when a writing is put in evidence, it must have effect according to its terms, and parol evidence is not admissible to give it a different construction, or to defeat its operation according to the import thereof; or even if the writing is ambiguous, it cannot be explained by other evidence, if the ambiguity is intrinsic, that is, if the phraseology is per se doubtful.

But if the ambiguity arises from something referred to but not fully expressed in the writing, explanation by other evidence is admissible. The latter is designated in law as a latent ambiguity, by which is meant that it does not appear upon the face of the instrument, but arises from something extrinsic. So also, when parties to a contract have undertaken to express it in writing, it will be assumed that they have expressed the whole, and nothing can be added by parol evidence, so far as relates to what the parties had in view at the time the contract was made. This is in effect saying that the written contract must speak for itself, and will be presumed to contain all that was intended at the time, though this contract may be varied by a subsequent parol agreement for good consideration. To the general rule as above stated there are, however, some qualifications. 1. It is admissible to explain the subject of the contract and all the circumstances which may properly be supposed to have been had in view by both parties, for the purpose of understanding the phraseology which they may have used. 2. Terms peculiar to a science, profession, art, or trade may be explained by witnesses conversant therewith. 3. Parol evidence is admissible to impeach a written instrument, by showing fraud, illegality of the subject matter, or whatever would operate in law to avoid it.-The admissibility of evidence is in judicial proceedings a matter of law, and in jury trials is determined by the court.