Mass. Gen. Laws ch. 146, § 47: Prima facie evidence of violation of statute

Section 47. If such steam engine or boiler or an appurtenance thereof is found to be in charge of, or operated by, a person not duly licensed as an engineer or fireman, and, after a lapse of one week from such time, it is again found to be so operated by an unlicensed person, it shall be deemed prima facie evidence of a violation of the preceding section.