No two sorts of birds practice quite the same sort of flight. The varieties are infinite（无限的）. But two classes may be roughly（粗糙地） seen. Any ship that crosses the Pacific（太平洋） is accompanied（陪伴） for many days by the smaller albatross, which may keep company with the vessel（船） for an hour without visible（可见的） or more than occasional（偶然的） movement of wing. The currents（（水） of air that the walls of the ship direct upwards（ 向上）, as well as in the line of its course, are enough to give the great bird with its immense（极广大的） wings sufficient（充分的） sustenance（食物） and progress. The albatross is the king of the gliders（滑行(或物)）, the class of flyers which harness（治理） the air to their purpose, but must yield（屈服） to its opposition（反对）.