The lecture was given, of course, specimen in hand, the various inhabitants of the branch of seaweed giving their evidence in succession of their own structure and way of life. To these living illustrations were added drawings on the blackboard to show the transformations of the animals, their embryological history, &c.[3] Since the lecture, Captain Bradbury has fitted up a large tank as an aquarium, where any specimens taken during the voyage may be preserved and examined. Mr. Agassiz is perfectly happy, enjoying every hour of the voyage, as well he may, surrounded as he is with such considerate kindness. _April 6th._—Though I took notes, as usual, of the lecture yesterday, I had not energy enough to enter them in my journal. The subject was the Gulf Stream,—the stream itself this time, not the animals it carries along with it. Mr. Agassiz’s late observations, though deeply interesting to himself, inasmuch as personal confirmation of facts already known is always satisfactory, have nothing novel now-a-days; yet the history of the facts connected with the discovery of the Gulf Stream, and their gradual development, is always attractive, and especially so to Americans, on account of its direct connection with scientific investigations carried on under our government. Mr. Agassiz gave a slight sketch of this in opening his lecture. “It was Franklin who first systematically observed these facts, though they had been noticed long before by navigators. He recorded the temperature of the water as he left the American continent for Europe, and found that it continued cold for a certain distance, then rose suddenly, and after a given time sank again to a lower temperature, though not so low as before. With the comprehensive grasp of mind characteristic of all his scientific results, he went at once beyond his facts. He inferred that the warm current, keeping its way so steadily through the broad Atlantic, and carrying tropical productions to the northern shores of Europe, must take its rise in tropical regions, must be heated by a tropical sun.[4] This was his inference: to work it out, to ascertain the origin and course of the Gulf Stream, has been, in a great degree, the task of the United States Coast Survey, under the direction of his descendant, Dr. Bache.”[5] We are now fairly in the tropics. “The trades” blow heavily, and yesterday was a dreary day for those unused to the ocean; the beautiful blue water, of a peculiar metallic tint, as remarkable in color, it seemed to me, as the water of the Lake of Geneva, did not console us for the heavy moral and physical depression of sea-sick mortals. To-day the world looks brighter; there is a good deal of motion, but we are more accustomed to it. This morning the lecture had, for the first time, a direct bearing upon the work of the expedition. The subject was, “How to observe, and what are the objects of scientific explorations in modern times.”