The enclosed premises and the lands adjoining the same belonging to any one of the state hospitals are hereby declared private grounds; and if any person be found thereon without authority, permission or good excuse, he shall be deemed a trespasser, and, on conviction thereof, shall be fined not exceeding $25; and if it shall appear that he was thereon for any unlawful or immoral purpose, in addition to being fined, he shall be imprisoned not exceeding sixty days.