Braley, J.
The plaintiff seeks under the St. of 1906, c. 463, Part II, § 247, to recover damages for the destruction of a barn with its contents, alleged to have been caused by fire directly communicated by the locomotive engine of the defendant. But if the loss is unquestioned the parties were at issue as to the origin *11of the fire. The defendant could show by relevant testimony, that it originated from other independent causes even if the circumstantial evidence introduced by the plaintiff seems to have been clear and abundant, that the ignition of the roof, from which apparently the fire spread through the building, must have been from sparks emitted by the engine. Perley v. Eastern Railroad, 98 Mass. 414. The defendant contends, that if its offer of proof had been admitted in evidence the jury would have been warranted in finding the fire had been set by a son of the plaintiff, or at least sufficient doubt would have been raised as to its liability to have overcome the burden of proof. But in the absence of any direct evidence connecting him with the occurrence, the defendant endeavored to show from incidents in his early life, that he had acquired a disposition which had ripened into a habit to set incendiary fires whenever the opportunity offered. A habit of this character is abnormal, and it may be criminal. The defendant was required to satisfy the presiding judge, that the course of conduct on which it sought to predicate the commission of an affirmative wrongful act of the character claimed had become so continuous and systematic that the setting of the fire in question would follow as a reasonable and probable consequence. Shailer v. Bumstead, 99Mass. 112. Thayer v. Thayer, 101 Mass. 111, 113, 114. Commonwealth v. Abbott, 130 Mass. 472, 473. Hathaway v. Tinkham, 148 Mass. 85. Lane v. Moore, 151 Mass. 87, 90. Edwards v. Worcester, 172 Mass. 104. Wigmore on Evidence, §§ 92, 376. If as a young boy he exhibited a strong inclination to set fires, and while still a youth did in several instances set them, proof of these instances would not raise a reasonable presumption that he had destroyed his mother’s property wantonly, even if at the time he is shown to have been living at home. It would not follow from common experience, that because on some occasions in the past he may have done a particular thing in a particular manner, that upon another and different occasion he would act in the same way. Robinson v. Fitchburg & Worcester Railroad, 7 Gray, 92, 95. Lewis v. Smith, 107 Mass. 334. Peverly v. Boston, 136 Mass. 366. It is because of this variability and uncertainty in the manifestations of individual conduct, even where the circumstances may be more or less uniform, that while an employee’s general reputation for incompetency in the performance of work for which he has been engaged *12is admissible, if the employer knew or by the exercise of reasonable diligence should have known of it, single instances of carelessness are inadmissible. Cooney v. Commonwealth Avenue Street Railway, 196 Mass. 11, 14, and cases cited. The defendant moreover, if it had been permitted to litigate the likelihood of his conduct by going at large into proof of alleged instances of previous fires, would have presented collateral issues which would have seriously embarrassed and prejudiced the plaintiff, and tended to confuse and mislead the jury. Emerson v. Lowell Gas Light Co. 3 Allen, 410, 417. Darling v. Stanwood, 14 Allen, 504, 508. Hill Manuf. Co. v. Providence & New York Steamship Co. 125 Mass. 292, 303. Commonwealth v. Jackson, 132 Mass. 16, 20. Commonwealth v. Ryan, 134 Mass. 223, 224. Reeve v. Dennett, 145 Mass. 23, 28. Lane v. Moore, 151 Mass. 87, 90. Commonwealth v. Hudson, 185 Mass. 402. The subsequent incendiary fires for which the son may have been responsible as well as his admission of having set some of them, were occurrences having no connection with the plaintiff’s cause of action. Commonwealth v. Campbell, 7 Allen, 541. And the further offer that “the district court . . . ordered an examination by two physicians, who committed him to the hospital on the ground that he had a mania for setting fires” must be construed as an offer of the record of judicial proceedings to which she was not a party or a privy. McDowell v. Connecticut Fire Ins. Co. 164 Mass. 394. We are therefore of opinion that the judge in his discretion properly excluded the offer of proof.
Exceptions overruled.