But the arts by which these new men of science contrived to evade the ignorance and the despotic limitations of their time, the inventions with which they worked to such good purpose upon their own time, in spite of its restrictions and oppositions, and which enable them to 'outstretch their span,' and prolong and perpetuate their plan for the advancement of their kind, and compel the future ages to work with them to the fulfilment of its ends;--the arts by which these great original naturalists undertook to transfer in all their unimpaired splendour and worth, the collections they had made in the nobler fields of their science to the ages that would be able to make use of them;--these are the arts that we shall have need to master, if we would unlock the legacy they have left to us. The proof of the existence of this special art of delivery and tradition, and the definition of the objects for which it was employed, has been derived thus far chiefly from sources of evidence exterior to the works themselves; but the inventors of it and those who made use of it in their own speech and writings, are undoubtedly the persons best qualified to give us authentic and lively information on this subject; and we are now happily in a position to appreciate the statements which they have been at such pains to leave us, for the sake of clearing up those parts of their discourse which were necessarily obscured at the time. Now that we have in our hands that key of _Times_ which they have recommended to our use, that knowledge of times which 'gives great light in many cases to true interpretations,' it is not possible any longer to overlook these passages, or to mistake their purport.