Mass. Gen. Laws ch. 161, § 100: Heating railway cars

Section 100. The department shall require every street railway company to heat its cars, when in use for the transportation of passengers, at such times, by such means, and to such extent, as the department shall determine, and the company shall forfeit twenty-five dollars for each trip run by any of its cars not so heated, except in case of accident to the heating process or apparatus, or other unavoidable cause. The state police shall cause this section to be enforced.