Railroad trains for the carriage of passengers must stop at all stations advertised by the railroad company as stops for such trains at least half a minute for receiving passengers thereon; and every railroad company and employee of such company, violating, or causing or permitting any violation of the provisions of this section, forfeits to the state, for the use of the public schools, not less than $25.00, nor more than $100.00, which may be recovered in the district court of the county in which such violation occurs. The conductor of the train shall be held prima facie to have caused any such violation occurring on the train in his charge. The company whose agent shall cause or permit such violation shall also incur and be liable for such forfeiture.