Ames, J.
The effect, and as may reasonably be supposed the purpose, of the cross-examination of the witness, Miles, was to bring before the jury the contents of the letter from Rawson. The letter was admitted, not in order to explain, or to throw any light upon any conversation in which Miles took part, but for the purpose of contradicting him, and for no other purpose. So far as we can judge from the bill of exceptions, the only contradiction of his testimony was in that part of it in which he said that no such letter had been shown to him, or that he did not remember seeing such a letter. Nothing is disclosed in the report having any tendency to make the letter a part of the conversation, and in that respect the case differs from Commonwealth, v. Vosburg, 112 Mass. 419, which is cited and relied upon by the plaintiffs.
*336It is a well settled rule that a witness cannot be cross-examined as to any fact, which is collateral and irrelevant to the issue, merely for the purpose of contradicting him by other evidence, if he should deny it. 1 Greenl. Ev. § 449. As to any such fact his answers are conclusive. The authorities to this effect are numerous. Farnum v. Farnum, 13 Gray, 508. Commonwealth v. Cain, 14 Gray, 7. Fletcher v. Boston & Maine Railroad, 1 Allen, 9. We see no possible ground upon which the letter from Rawson could be said to be otherwise than collateral and irrelevant. It was merely the expression of Rawson’s opinion as to the merits of the plaintiffs’ case. But Rawson was not an agent for the defendant and had nothing to do with this policy of insurance. The purport of the letter was that the companies which he represented had paid the amounts which they had insured upon the same property, and that he, Rawson, saw no reason why the defendant should not do the like. But as the defendant had nothing to do with Rawson, and was not bound by his judgment, it was wholly immaterial whether its agent Miles had or had not seen his letter. As the tendency of the letter was to show that the defendant was unreasonably resisting a claim which other insurance companies had found upon investigation to be well founded and meritorious, its admission in evidence could not fail to be prejudicial to the defendant. Exceptions sustained.