One of the most terrible steamboat explosions which has taken place in a great number of years, occurred on the 13th inst., near Memphis, Tann., on the steamboat Pennsylvania, while on her passage from New Orleans to St. Louis. There were 450 passengers on board, and no less than 250 are reported to have lost their lives. The boilers exploded with great violence, the boat then took fire, and burned to the water's edge. During the past three years very few explosions have taken place on the western rivers, and river traveling had become as safe as at the East. This was, no doubt, owing to the vigilance of the Steamboat Inspectors. This year the explosions have been frequent and disastrous, and the western steamboats are again fast earning their old character of "floating coffins." There must be something Wrong in regard to the manner in which the provisions of the new steamboat law for the protectio" of life is carried out. On the same day in which the above explosion took place, the steamer Eclipse exploded her heater when near Natchez, Miss., by which accident two persons were killed, and three dangerously wounded.