Messrs. Eaton & Gilbert, of Troy, have built a beautiful car for the Hudson River Railroad, which is divided into state rooms of eight feet square. The car is 45 feet long and 9i wide ; each room is calculated for a family or a party, and is furnished with one sofa, four chairs, a looking-glass, and small centre-table. The panels are painted in landscape, the ceiling hung with silk, and the floor richly carpetted. The rooms are entered by a side passage, andfcach is well lighted and ventilated. There is a wash-room in the front part of the car. Altogether, it isjde-signed to meet the wants for which separate state-rooms are provided on our steamboats. It is the first experiment of the kind, we believe, upon any railroad in om country, and it successful, more cars of the same kind will be provided for this line, and other railroads will also adopt them. We are doubtful about the experiment paying yet, but it will do so before many years pass away. A family or [ party will not pay an extravagant price for a separate room, when the journey is only for a few hours, but they will do so, it they have to travel for a number of hours at once.