The Great Professor has given the first Monograph of his _Magnum Opus_ to the Great Republic and the wider realm of Science. The learned world resolves itself into committees to consider every important work; claiming leave to sit for as long a time as they choose,--for years, or for a whole generation. Every alleged fact is to be verified or cancelled or qualified, every inference to be measured over and over again by its premises, every proposition to be tried by all the tests that can prove its strength or weakness, and the whole to be marshalled to the place it may claim in the alcoves of the universal library. No hasty opinion can anticipate this final and peremptory judgment. Its elements must of necessity be gathered slowly from many and scattered sources. The accumulated learning of the great centres of civilization, the patient investigation of plodding observers, the keen insight of subtile analysts, the jealous clairvoyance of dissentient theorists, the oblique glances of suspicious sister-sciences, the random flashes that skepticism throws from her faithless mirror to dazzle all eyes that seek for truth; through such a varied and protracted ordeal must every record that embodies long and profound observation, large and lofty thought, reach the golden _Imprimatur_ which is its warrant for immortality. The work of Mr. Agassiz, if we may judge it by the portion now before us, has a right to challenge such a matured opinion, and to wait for it. Not the less does a certain duty belong to us as literary journalists with reference to these stately volumes, which are in the hands of thousands, learned and unlearned, and of which there are scores of thousands waiting to hear. Our duty we consider to be four-fold: first, that of recognition in terms of fitting courtesy; secondly, of analysis for the general reader; thirdly, of accentuation, so to speak, of what seems most widely applicable or interesting; and lastly, of making such comments as so pregnant a text may suggest. And first, of recognition. Here are the fruits of ten years of patient labor, taken out of the heart of life, in the age of vigor, which is that of ambition,--to use the phrase of another great observer,--by a man of large endowments and of vast knowledge, assisted by skilful collaborators, by finished artists, by the counsels and liberality of the learned few, and the generous countenance of the intelligent many. Before analysis, before criticism, there should be uttered a welcome; not grudging, not envious of an overshadowing reputation, not over-curious in searching for qualifications to abate its warmth, not carefully taming down its enthusiasm to tepid formalisms; but full-souled and free-spoken, such as all noble works and deeds should claim.