This is an action to recover for personal injuries received by the plaintiff while a passenger on one of the defendant’s cars, which resulted from the same explosion as is considered in Guinan v. Famous Players-Lasky Corp., ante, 501, decided this day. The cases were tried together and the *527jury returned a verdict for the railway company. The case is before us on a report of the trial judge, and presents a single question relating to evidence.
There was evidence that the plaintiff was a passenger on the car; that one Shirley boarded the car at Pleasant Street in Boston, carrying with him a burlap bag containing scrap moving picture film; that he placed the bag at a distance from the heating apparatus in the car that varied with the testimony of the different witnesses, some testifying that the bag touched the heater, and others that it was from one to two feet from it. One Galvin, a passenger on the car, testified that as it proceeded from Boylston Street toward Park Street in the subway “a flash of flame came out of the heater in the car and the burlap bag became ignited; that the flash of flame came from the heater to the burlap bag; that then the flames burst out all over the street car . . . .” An electrical engineer and employee of the defendant testified as to the construction of the heater, and the mechanical and electrical devices which permitted electrical energy to heat the car through its operation.
One Hewitt, called by the plaintiff, qualified as an expert on the heater in question, “but having no expert knowledge of films,” the trial judge refused to permit him to testify. The plaintiff excepted to this ruling.
The rule is well established that whether a person called as an expert has the necessary qualifications to testify is a preliminary question to be decided by the trial judge; and his decision is conclusive, unless it appears on the evidence to have been erroneous as matter of law. Perkins v. Stickney, 132 Mass. 217, 218. White v. McPherson, 183 Mass. 533, 534. Old Silver Beach Corp. v. Falmouth, 266 Mass. 224, 226. In dealing with evidence of this character it was said by Chief Justice Shaw in New England Glass Co. v. Lovell, 7 Cush. 319, at page 321: “It is not because a man has a reputation for superior sagacity, and judgment, and power of reasoning, that his opinion is admissible .... But it is because a man’s professional pursuits, his peculiar skill and knowledge in some department of science, not common to men in general, enable him to draw an inference, where men *528of common experience, after all the facts proved, would be left in doubt.” The competency of a witness offered as an expert lies largely, although not exclusively, within the discretion of the presiding judge. Commonwealth v. Spencer, 212 Mass. 438, 448. Jordan v. Adams Gas Light Co. 231 Mass. 186, 189. Johnson v. Lowell, 240 Mass. 546, 549. Olsen v. New England Fuel & Transportation Co. 251 Mass. 389, 393.
The trial judge was warranted upon the evidence in concluding that the issue was not whether a heater alone would cause the flame, but whether a heater in proximity to a highly inflammable substance might cause the flame. As it did not appear that the witness had any expert knowledge of the chemical properties, composition and inflammability of motion picture film, the trial judge in his discretion was warranted in ruling that the witness was not qualified to testify as to the cause of the flash of flame. No abuse of discretion on the part of the judge having been shown, that exception cannot be sustained. Carroll v. Boston Elevated Railway, 200 Mass. 527, 533. Hines v. Waltham Manuf. Co. 208 Mass. 282, 284. Mann v. Scituate, 260 Mass. 592, 593.
In view of the conclusion reached that there was no error in the exclusion of the proffered testimony for the reasons stated, it is unnecessary to consider whether it was properly excluded on other grounds argued by the defendant.
Judgment on the verdict.