The test to determine the competency of evidence is not to inquire how the facts were brought to the attention of the triers, but whether they were capable of siding them. It follows, therefore, that any prejudicial fact that is not relevant to one of the various issues in the case (using "issue" as it is used in Darling v. Westmoreland, 52 N.H. 401, and not as in King v. Chase, 15 N.H. 9) is inadmissible as matter of law. This is true whether the evidence is introduced to prove the defendants' fault to discredit a witness. The court, therefore, erred in permitting the plaintiff to show that the employers of the witness were the real defendants, unless his credibility was in issue. The test to decide that question is to inquire whether there was any contest on the part of the plaintiff as to the truth of his testimony — not whether he was hostile or friendly. It must be held, therefore, that the credibility of the witness was not in issue; for the plaintiff does not contend that the testimony was false, or that he was surprised by it. The fact that the credibility of the witness was not in issue distinguishes this case from Genest v. Company,75 N.H. 509.
The plaintiff also seeks to justify his cross-examination of the witness on the ground of his hostility. If it can be found that the witness was hostile, within the meaning of the rule which permits a party to cross-examine a witness called by him, it does not help the plaintiff; for the purpose of such a cross-examination is to aid the triers in their search for the truth. Therefore, the exception to the ruling permitting the plaintiff to cross-examine the witness raises the question whether it could be found that such procedure would *Page 59 aid the jury, and all fair-minded men must agree that it cannot be so found. In other words, all fair-minded men must agree that permitting the plaintiff to cross-examine the witness for the sole purpose of showing that his employers were the real defendants could not aid the jury in their search for the truth. The evidence was therefore erroneously admitted in any view of the law, whether it was admitted as a matter of right or as matter of discretion; for it was not only incapable of siding the jury, but was calculated to direct their attention to prejudicial facts. In fact, the latter was the sole purpose for which the evidence was introduced.
There must, therefore, be a new trial unless the court's instructions limiting the application of the evidence to the issue of credibility remedied the error. It cannot be held, however, that those instructions prevented the evidence from having its intended effect; for since the credibility of the witness was not in issue, the instructions limiting the applicability of the evidence could not aid the jury, but tended to confuse and mislead them.
Exception sustained.
All concurred. *Page 60