THE task which I have undertaken this evening—to give a general sketch, however slight, of the work and results of the Challenger expedition in the space of a single lecture—is by no means an easy one, for two reasons. The various lines of inquiry bear on so many different subjects, and these dovetail into one another in such a complicated manner, that it would take many hours to explain them even in the most superficial way. The other reason is that the observations which were made during the Challenger expedition have only as yet been very imperfectly examined, and only half digested, owing to want of time, and the great collections in natural history which were brought home in the ship have been only glanced at, and it is therefore scarcely sale for me to use either the observations or the collections as the bases of generalisation. I must therefore this evening, in this address, only be regarded as giving a most elementary idea of the objects of the expedition and its results, and what I say must be regarded as preliminary, and subject to further reconsideration. Still, some new and remarkable facts and phenomena which have hitherto been unknown, or only vaguely guessed at, are sumciently definite, and I will devote the short time at my disposal to the consideration of one or two of these. The superficial area of this world of ours is about 197,000,000 of square miles, and of these about 140,000,000 are covered by the blue sea at an average depth of 2,500 fathoms—about 15,000 feet. This vast region under the sea has not until comparatively recently excited much curiosity. It seemed to be practically inaccessible, and certain hasty and incorrect assumptions in regard to some of its conditions had reduced it to a barren uniformity and divested it of any interest. The laying of deep-sea cables for the purposes of ocean telegraphy, by bringing to light certain phenomena which threw a doubt upon previous conclusions, stimulated inquiry, and gave rise to new speculation; and the systematic scientific exploration of the depths of the sea by several special exploring expeditions put our knowledge upon a totally different footing. We now know that the sea covers a vast region which is to a certain degree comparable with the land—a region which has its hills, valleys, and great undulating plains; that it has its various soils—widely different materials laid down and accumulated in different places; that it has its climates, whatever the very exceptional conditions of those climates may be; and that it has its special races of inhabitants which depend, like the inhabitants of the rest of the world, upon the conditions of climate and on the nature of the soil for their distribution.